Responsa for Bava Batra 294:3
ומי אמר רב נחמן הכי והא אמר רב נחמן אע"ג דאמר שמואל המוכר שטר חוב לחבירו וחזר ומחלו מחול ואפילו יורש מוחל מודה שמואל שאם נתנו במתנת שכיב מרע דאינו יכול למוחלו
Samuel, [nevertheless]. admits that if he presented it to him as the gift of a dying man, he cannot [subsequently] remit it.<span class="x" onmousemove="('comment',' B.K. 92a; B.M. 20a; Kid. 38a. ');"><sup>9</sup></span> [Now]. if it is agreed'<span class="x" onmousemove="('comment',' Lit., 'you said'. ');"><sup>10</sup></span> that [this<span class="x" onmousemove="('comment',' The validity of the verbal gift of a dying man. ');"><sup>11</sup></span> is] Biblical, one can well understand the reason why one cannot remit [the debt]; if, however, It is maintained<span class="x" onmousemove="('comment',' Lit., 'you said'. ');"><sup>10</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.