Reference for Bava Kamma 205:1
אין כופין את המוכר למכור זימנא אחריתי ואם אמר לו על מנת כופין את המוכר למכור
[such as] the Exilarch<span class="x" onmousemove="('comment',' [MS.M. omits 'the Exilarch'; in curr. edd. it is bracketed.] ');"><sup>1</sup></span> he cannot compel the vendor to sell it to him again. But if when buying it he explicitly made this stipulation he could compel the vendor to sell it to him again.<span class="x" onmousemove="('comment',' V. p. 596, n. 2. ');"><sup>2</sup></span> The Master stated: 'If one man buys a field in the name of another [such as] the Exilarch, he cannot compel the vendor to sell it to him again'. But is this not quite obvious? — You might, however, have said that the vendee could argue: 'You very well knew that I was taking the field for myself, and that [in buying it in the name of the other person] I merely wanted protection, and as I was surely not prepared to throw away money for nothing I undoubtedly made the purchase on the understanding that a new deed should be drawn up for me [by you].' It is therefore made known to us that the vendor can retort to him: 'It is for you to make arrangements with the person in whose name you bought the field that he should draw up for you a new title deed.' 'But if when buying it he explicitly made this stipulation he could compel the vendor to sell it to him again.' But is this not obvious? — No, it is required to meet the case where the vendee said to the witnesses in the presence of the vendor: 'You see that I want another deed.' You might in this case think that the vendor could say to him: 'I thought that you referred to a deed to be drawn up by the one in whose name you bought the field'; it is therefore made known to us that the vendee can reply to him: 'It was for that purpose that I took the trouble and stated to the witnesses in your own presence, [to show] that it was from you that I wanted the other deed.'