Reference for Bava Batra 337:9

ולכתוב להאי שטרא מעליא ולכתוב תברא למוכר כל שטרי דיפקון על ארעא דא פסולין לבר מן דיפוק בזמנא דא

to say to the creditor, 'Wait until I am firmly established in the possession of this land'?<span class="x" onmousemove="('comment',' Lit., 'in this land and I will be established in it'. ');">²⁹</span> This<span class="x" onmousemove="('comment',' R. Safra's law. ');">³⁰</span> [surely], could be derived [from the fact] that since he<span class="x" onmousemove="('comment',' The buyer. ');">³¹</span> holds two deeds he [can] seize [once] and [immediately] seize again!<span class="x" onmousemove="('comment',' Why, then, the necessity for postponing the seizure of the second field to a later date. ');">³²</span>

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