Reference for Bava Batra 267:5
אמרו חכמים כל מתנה שאינה שאם הקדישה מוקדשת אינה מתנה:
the Sages said: Any gift which is not [of such a character] as would [allow it to] become sacred when [the recipient] consecrated it, is not a [proper] gift.<span class="x" onmousemove="('comment',' From this it follows that a gift which is dependent on certain conditions is not legally valid. Shammai, drawing an analogy between this case and that of Jonathan, where the father was manifestly determined that his sons shall have no benefit from his estate, disputed the legality of the return of the third to the sons. Though the father's condition was not explicit it was sufficiently implicit, in the opinion of Shammai, to render the gift to Jonathan entirely dependent on its fulfilment. Jonathan by his reply pointed out to Shammai that the gift to him could not possibly he regarded as conditional, since it was generally conceded that he was fully entitled to sell it and to consecrate it and to dispose of it in any way he liked. [For a different version of the story, v. J. Nedarim, v. 6]. ');"><sup>9</sup></span> Our Rabbis taught:<span class="x" onmousemove="('comment',' Suk. 28a. ');"><sup>10</sup></span>