Responsa for Bava Batra 273:7
מאי טעמא אמר אביי מתנת שכיב מרע לא קנה אלא לאחר מיתה וכבר קדמו אחריך
R. Johanan said: The <i>halachah</i> is according to Rabban Simeon b. Gamaliel, who [however], admits that if [the estate] was assigned<span class="x" onmousemove="('comment',' By the first recipient. ');"><sup>19</sup></span> as the gift of a dying person, the transaction is invalid.<span class="x" onmousemove="('comment',' And the second beneficiary may reclaim it from the donee. ');"><sup>20</sup></span> What is the reason? — Abaye said, [because] the gift of a dying person is acquired only after death, and [by that time] 'after you'<span class="x" onmousemove="('comment',' I.e., the second beneficiary, with reference to whom the original owner and testator had said to the first beneficiary, 'after you it shall be given' etc. ');"><sup>21</sup></span>
Teshuvot Maharam
A. Since C did not marry before A's death, and since the money never came into C's possession, it never belonged to C, and A's widow is, therefore, entitled to collect her ketubah from that money. A widow is entitled to collect her ketubah from all bequests made causa mortis, and from all gifts that are not legally to be delivered to the donee (as in cases where the donor died before the stipulated date of delivery of the gift) but which must be so delivered for the reason that "it is a meritorious act to fulfill the expressed wishes of a dying person" (Gittin, 15a).
SOURCES: Pr. 966; Mord. B.B. 629.