Quotation על בבא בתרא 264:1

One who is about to die who assigns his property in writing [to another]: If he retains any land [for himself] however small, he renders his gift valid. But if he retains no land whatsoever, his gift is not valid. One who assigns in writing his property to his children, and he assigns to his wife in writing any plot of land, however small, she lost her ketubah. Rabbi Yose says: if she accepted [such an assignment] even though he did not assign it to her in writing she lost her ketubah.