Responsa for Bava Batra 293:4
א"ר זירא אמר רב מנין למתנת שכיב מרע שהיא מן התורה שנאמר (במדבר כז, ח) והעברתם את נחלתו לבתו יש לך העברה אחרת שהיא כזו ואי זו זו מתנת שכיב מרע
[which<span class="x" onmousemove="('comment',' The superfluity of the expression of [H] or, according to others, of [H] ');"><sup>9</sup></span> implies that] there exists another transfer which is [the same] as this [one]. And which is it? It is the gift of a dying man.<span class="x" onmousemove="('comment',' As the transfer of a father's estate to a daughter takes place without symbolic acquisition so does the transfer of the gift of a dying man. ');"><sup>10</sup></span> R. Nahman in the name of Rabbah b. Abbuha said: [It may be derived] from the following.<span class="x" onmousemove="('comment',' Lit., 'from here'. ');"><sup>11</sup></span>
Teshuvot Maharam
A. A dowry gift becomes the property of the donee only if the marriage takes place. Therefore, neither A nor his daughter has ever gained title to B's money, and A must return the principal plus the interest to B. Even if B expressly stipulated that he will forfeit the 15 pounds if the marriage does not take place, such a stipulation is considered an Asmakhta and is not valid. B, however, must pay A for his trouble in managing B's investments.
SOURCES: Cr. 86; Pr. 285; Mord. B.B. 615; Agudah B.B. 198.