daf bit: Bava Batra 153

We previously learned that if a sick man makes a gift and then recovers, there are cases where the gift can be rescinded. What if there is a disagreement -- he says "I was sick and recovered" and the recipient says "you were in perfect health" (in which case the gift would certainly stand)? Rabbi Meir says the giver must prove he was sick; however, the sages say the burden of proof is on the claimant. (153a)