I had this thought a few weeks ago - don't know if it came from someone else or is my own:
If someone showed me proof of the existence of a god, I would cease to be an atheist, but I would still be a humanist.
I think it's a brilliant thought, and a very snappy expression of one reason I like to think of myself as a humanist rather than as an atheist.
But I don't want to go around claiming credit for it if I actually heard it from someone else, and just forgot the source. I haven't been able to find it online (using relevant Google searches), but that doesn't mean I couldn't have heard it somewhere, or read it in a physical book.
So this is a plea to any well-read, knowledgeable reader to let me know: have you heard this somewhere else, and can you tell me who first came up with it?