Reference for Bava Metzia 187:15

<br><br><big><strong>הדרן עלך השוכר את הפועלים</strong></big><br><br>

AND WHATEVER CAN BE FULFILLED EVENTUALLY etc. R. Tabla said in Rab's name: This is the view of R. Judah b. Tema. But the Sages say: Even if it is impossible to fulfil it eventually, and one stipulates it at the beginning, the stipulation is valid. For it has been taught: [If one says,] Here is thy divorce, on condition that thou ascendest to Heaven or descendest to the deep, on condition that thou swallowest a hundred cubit cane or crossest the great sea on foot; if the condition is fulfilled, the divorce is valid, but not otherwise.<span class="x" onmousemove="('comment',' I.e., it is assumed that he meant the act to be invalid. ');">¹³</span>

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