Okay. Thanks to
@Faolyn for providing the quote.
I thought you were talking the default of 5e. The default is for divine power to only come from gods. The DMG, though, provides a ton of ideas on different ways for the DM to run things in his game, and that's definitely one way to do it. As I said, I would allow it in my game. However, if instead of asking me if it was okay, a player showed me that passage and then expected to be able to play a non-deity focused cleric, I'd be really annoyed at his temerity.