I think an absolute rule is a bit much. I also think that a better rule is one more focused on the actual problem, rather than the perceived one. A more focused rule will also lead to less concern over what counts as "rules referencing". Players referencing the rules is not a problem if the referencing occurs during other people's turns and they are ready to go on their own turn.
The actual problem seems to be people looking up details of their spells after their turn starts instead of having their spells ready. It might also be a problem if people look up the rules when it's their turn or try to hold up the game until they can get the rule to cite.
I think rules such as:
You must have the text of any spell you cast (and any monsters you summon, animal companions you have, etc.) out and ready to be read at the start of your turn.
You must have printed copies of your commonly used spells/rules (spells if you're a caster, grapple/disarm/bull rush if your character is built for them, turn undead if you're a cleric, etc.) as part of your character sheet.
If you are unsure of a rule that will affect your action, either look it up before your turn so that you have it ready, or make do without it.
If you are performing an action that might require the GM to look up the rules, keep the rule out and open, do not just read it yourself and then close the book before your turn.
The actual problem seems to be people looking up details of their spells after their turn starts instead of having their spells ready. It might also be a problem if people look up the rules when it's their turn or try to hold up the game until they can get the rule to cite.
I think rules such as:
You must have the text of any spell you cast (and any monsters you summon, animal companions you have, etc.) out and ready to be read at the start of your turn.
You must have printed copies of your commonly used spells/rules (spells if you're a caster, grapple/disarm/bull rush if your character is built for them, turn undead if you're a cleric, etc.) as part of your character sheet.
If you are unsure of a rule that will affect your action, either look it up before your turn so that you have it ready, or make do without it.
If you are performing an action that might require the GM to look up the rules, keep the rule out and open, do not just read it yourself and then close the book before your turn.