The first reference I see to the Weave is in the 1996 late 2e
Faiths & Avatars when FR was firmly its own separate sphere in the Spelljammer cosmology (The Spelljammer Realmspace book came out in 1991).
Page 15: "Mystra died at Helm’s hand on the Celestial Staircase, trying to gain access to her home plane. Before she battled Helm, she had transferred a great deal of her power into her Chosen, Azuth, the Magister, and Elminster. As she died, she gave Midnight the pendant with some of her essence and spread the remainder of her power into
the magical weave that surrounds and permeates Realmspace."
I don't see references to the Weave in the 1e Campaign Setting, the 2e FR Adventures book (though it talks about some unique aspects of FR magic like mage sigils) or the 2e campaign setting. It could have come up in an earlier dragon article or secondary sourcebook though.
Faiths & Avatars goes on to say that the Weave is part of Mystra's divine portfolio along with magic and spells. In her god entry it says "She provides and tends
the Weave, the conduit to enable mortal spellcasters and magical crafters to safely access the raw force that is magic."
In the
3.0 Campaign Setting it has a section on the weave on page 15:
The Weave
Mortals cannot directly shape raw magic. Instead, most who wield magic make use of the Weave. The Weave is the manifestation of raw magic, a kind of interface between the will of a spellcaster and the stuff of raw magic. Without the Weave, raw magic is locked away and inaccessible—an archmage can’t light a candle in a dead magic zone. But, surrounded by the Weave, a spellcaster can shape lightning to blast her foes, transport herself hundreds of miles in the blink of an eye, even reverse death itself. All spells, magic items, spell-like abilities, and even supernatural abilities such as a ghost’s ability to walk through walls, depend on the Weave and call upon it in different ways.
The exact nature of the Weave is elusive because it is many things simultaneously. The Weave is the body of Mystra, the goddess of magic. Mystra has dominion over magic worked throughout Toril, but she cannot shut off the flow of magic altogether without ceasing to exist herself. The Weave is the conduit spellcasters use to channel magical energy for their spells, both arcane and divine. Finally, the Weave is the fabric of esoteric rules and formulas that comprises the Art (arcane spellcasting) and the Power (divine spellcasting). Everything from the texts of arcane spellbooks to the individual components of spells is part of the Weave. Magic not only flows from source to spellcaster through the Weave, the Weave gives spellcasters the tools they need to shape magic to their purposes.
Whenever a spell, spell-like ability, supernatural ability, or magic item functions, the threads of the Weave intertwine, knit, warp, twist, and fold to make the effect possible. When characters use divination spells such as detect magic, identify, or analyze dweomer, they glimpse the Weave. A spell such as dispel magic smooths the Weave, attempting to return it to its natural state. Spells such as antimagic field rearrange the Weave so that magic flows around, rather than through, the area affected by the spell.
Areas where magic goes awry, such as wild magic zones and dead magic zones, represent damage to the Weave.
Also on page 55:
Mystra and the Weave
Open any three books describing the magic and mage lore of
Faerûn, and you’re apt to find three conflicting accounts of the
origins and true nature of magic. Some of this apparent contradiction
is deliberate falsehood designed to restrict the mastery of
magic to those beings properly trained. Much of the rest of it
arises from strange views or outright mistakes often unwittingly
reproduced by later scholars.
Hear now the truth of things, as best it is understood. To speak
simply, all known worlds and planes swarm with ever-present energies.
Large and small, free-flowing or bound by physical barriers or
magical effects (themselves merely energies shaped and designed to
restrict or hold other energies), these surges and dissipations of
energy give light and life and movement to everything. They are
the stuff of life itself, and they would be present even if all living
and once-living things on Toril were stripped away to bare rocks.
What some folk refer to as magic and wizards speak of as the
Art is the means by which some beings can call on the ever-present
energies and wield them to create effects. Sorcerers do this
instinctively through an innate gift and the incredible force of
their personalities. Bard songs waken echoes of the songs of beginning,
the music of creation itself. Wizards construct processes—
spells—enabling them to bend the Weave to their will in order to
do what they desire. The divine power infusing any cleric holding
the spells of her god or goddess can do the same, shaping the
Weave through the holy (or unholy) power granted her.
Many types of magic—rune magic, shadow magic (not to be
confused with the Shadow Weave), gem magic, elemental magic,
even the elven high magic of old—have been spoken of down the
years, but these are all merely different processes or paths to the
same mastery of natural energies. This endless, ever-shifting web
of forces is known as the Weave. Humans refer to the entity or
awareness that is bound to the Weave of Toril as Mystra, and worship
her as their goddess of magic.
The present Mystra is a recently ascended mortal woman, who
took over from her exhausted predecessor during the Time of
Troubles. Mystra exists to give magic to all creatures and to control
its use. In ancient times, the archmages of Netheril ignored
the dictates of Mystryl, goddess of magic at the time. One, the
wizard Karsus the Mad, tried to seize divinity by the casting of
mighty spells that would have wrecked Toril’s Weave. Mystryl sacrificed
herself to save the Weave. Her successor Mystra decreed
that no mortals would be allowed to wield such terrible magic
again—and that decree holds to this day.
Mystra wards the Weave against those powerful or reckless
enough to damage it further. Until the world changes or the
divine powers themselves lay down their guardianship over human
affairs, the high and perilous magic of the past remains locked
away under Mystra’s eye.
And then on page 57 you get discussion of the Shadow Weave:
The Shadow Weave
During the course of her eternal war with the goddess Selûne, the
goddess Shar created the Shadow Weave in response to Selûne’s creation
of Mystra and the birth of the Weave. If the Weave is a loose
mesh permeating reality, the Shadow Weave is the pattern formed
by the negative space between the Weave’s strands. It provides an
alternative conduit and methodology for casting spells.
And then on page 247 under Mystra's deity entry:
She provides and tends to
the Weave, the conduit that allows
mortal spellcasters and users of
magic to safely access the raw
force that is magic. Essentially,
Mystra is the Weave.
3e takes a more FR is its own universe perspective in its writing and does not really address spelljammer or FR connecting to other settings.
In
Magic of Faerun on pages 4-5 it says:
The Beginning
Clerics of Chauntea, Selûne, and Shar tell of the following legend.
Lord Ao created the universe that now holds the world of
Toril. After this creation, there was a period of timeless nothingness,
a misty realm of shadows that existed before light and
darkness were separate concepts. Eventually, this shadowy
essence coalesced to form twin beautiful deities, polar opposites
of each other, one dark and one light. The twin deities
created the bodies of the heavens and Chauntea, the embodiment
of the world Toril. Toril was lit by the cool radiance of
the deity Selûne, and darkened by the welcoming embrace of
the deity Shar, but no heat yet existed in this place.
Chauntea begged for warmth that she might nurture life
and living creatures upon her form, and this caused the
twin deities to become divided in intent. The two fought,
and from their divine conflict, the deities of war, disease,
murder, death, and others were created.
Selûne reached beyond the universe to a plane of fire,
using pure flame to ignite one of the heavenly bodies so
that Chauntea would be warmed. Shar became enraged and
began to snuff out all light and warmth in the universe.
Desperate and greatly weakened, Selûne tore the divine
essence of magic from her body and hurled it at her sister,
tearing through Shar’s form and pulling with it like energy
from the dark twin. This energy formed Mystryl, the deity
of magic. Composed of light and dark magic but favoring
her first mother, Mystryl balanced the battle enough to
establish an uneasy truce between the two sisters.
Shar, who remained powerful, nursed a bitter loneliness
in the darkness and plotted her revenge. Selûne waxed and
waned with the light, but drew strength from her allied
daughters and sons, and even interloper deities from other
planes. Their battle continues to this day.
Mystryl, Mystra, and Midnight
The birth of the being then known as Mystryl did more
than just balance the war between the sisters of light and
darkness. Her very existence changed the reality of the universe
by creating the Weave, the conduit that allows creatures
to use magic. Suddenly, rather than magic being
restricted to just the deities, any creature with the talent or
training could draw upon the power of magic through the
Weave. When sentient creatures appeared on Toril, some of
them learned to use the Weave while shamans and clerics
drew their magic directly from deities. Acknowledgement
of her gift led to worship, and Mystryl drew power from
that, becoming one of the more powerful deities.
THE MOMENT OF NO MAGIC
Mystryl’s duty was to tend and repair the Weave, but she
herself was so much more than that. Mystryl was the
embodiment of the Weave. It ebbed and flowed with her
moods, actions, and energy. Something that harmed the
Weave harmed Mystryl, and vice versa. Her ties to the
Weave were so strong that only she could fully understand
and protect it. When Karsus, a powerful arcanist from the
human civilization of Netheril, attempted to drain her
power in order to elevate himself to divinity, he found himself
unqualified for the task, and magic began to unravel all
over Faerûn. The severely crippled Mystryl chose to sacrifice
herself to save the Weave. Her death caused magic to
cease functioning across the universe, instantly slaying the
upstart Karsus. The deity was reborn as Mystra, and she was
able to repair the Weave so that such powerful magic was
no longer possible.
THE TIME OF TROUBLES
This new deity shared the same close ties with the Weave as
her predecessor. This was proven in the Year of Shadows
(1358 DR) when she was slain in Waterdeep in battle with
Myrkul and other powerful beings. When her essence
merged with the land, magic ran wild in some areas and
stopped completely in others. When the mortal wizard
Midnight assumed the mantle of divinity and the portfolio
of the fallen Mystra, magic as a whole returned to normal,
although many places still raged with chaotic surges and
others seethed with the cold tranquility of a dead magic
area. While many of these damaged portions of the Weave
have been repaired, enough remain to serve as a warning to
mortals—or deities—who would attempt to harm the
Weave or Mystra.
On page 7 it discusses the Shadow Weave
THE SHADOW WEAVE
Because she knows that striking directly against Mystra at
this time is foolish and dangerous, Shar chose an indirect
method to combat her traitorous daughter. If Mystra is the
source of all magic on Faerûn, making every mortal spellcaster
beholden to her to some extent, it would be possible
to steal away some of that power and the associated worship
by creating another source of magic that was under Shar’s
control and whose practitioners would have to be beholden
to her if they wished to survive its use unscathed.
Shar studied the Weave and used her own energy in
remote parts of the world to experiment on it, eventually
coming to understand how it worked and duplicating its
effects with her own subtle and dark creation. Eventually
this experiment grew to encompass the entire globe, although
none knew of its existence. This creation is the Shadow
Weave, a dark and distorted copy of the true Weave that
enhances the magic of shadows, enchantment, necromancy,
and illusion.
