Richard Pryor is quoted throughout the internet as saying, "The reason people use a crucifix against vampires is that vampires are allergic to bullshit", which can be found on his 1971 comedy album Craps (After Hours) at the end of the 10th track titled "Religion".
He also does standup routine making fun of religion:
http://www.dailymotion.com/video/xbwq56_richard-pryor-god_tech