daf bit: Bechorot 52

The torah tells us that land in Eretz Yisrael cannot be sold beyond redemption; during the Yovel (jubilee), every 50 years, all holdings return to their ancestral tribes. The mishna on today's daf discusses this, saying that the following do not return during the Yovel: the double share (inheritance) of the first-born; the inheritance from one's wife and of one who marries his sister-in-law; and a gift. These are the words of R. Meir. But the sages say that a gift is like a sale and does return, and R. Eleazar says all these return because (according to the g'mara) when property is divided among heirs it is like a sale. (52b)