If you can not find out where it is written it might be something gm invented.
Also if demons are too dangerous try devils.
but anyway if what you wrote is true then it means the laziest path to power is to not get class levels but instead get enough money from whichever opportunity you have to then get power.
Or maybe worship sloth: this way the training to get closer to your ideal and be a better cleric is to sit around doing nothing productive.