Reference for Bava Kamma 176:15
אמר ליה אביי אטו ברא ירית אבא אבא לא ירית ברא אלא לאברוחינהו לנכסי מבריה קא אתי הכא נמי לאברוחינהו לנכסי מאחוה אתי
cannot be compared to that stated in the Mishnah.' On what ground? — R. Joseph replied: We should have no difficulty if the case in the Mishnah were stated in a reversed order, i.e., 'If a son assigns his possessions to his father [to take effect after the son's death, and the father sold them during the lifetime of the son and died before the son,' and if the law would also in this case have been that the purchaser acquired title to the possessions] it would indeed have been possible to prove from it that a right to usufruct does not amount to a right to the very substance. But seeing that what it actually says is, 'If a father assigns his possessions to his son,' [the reason why the sale by the son is valid is] that [since] he was eligible to inherit him, [the father by drawing up the deed must necessarily have intended that the transfer to the son should have legal effect forthwith].<span class="x" onmousemove="('comment',' For if otherwise why was the deed necessary at all? [Whereas in the case of Samuel b. Abba, the deed was necessary for in the absence of one the estate would be inherited by the husband. V. B.B. 111b] ');"><sup>15</sup></span>