Commentary for Kiddushin 38:12
תניא אידך המוכר את בתו ופסק על מנת שלא לייעד נתקיים התנאי דברי ר"מ וחכ"א אם רצה לייעד מייעד מפני שהתנה על מה שכתוב בתורה וכל המתנה על מה שכתוב בתורה תנאו בטל
But they maintain: If he wishes to designate her, he can do so! - But, said R'Aha the son of Raba, it is analogous on the view of R'Jose son of R'Judah.<span class="x" onmousemove="('comment',' Rashi: just as her betrothal to the second is valid because her master did not designate her from the time he bought her, so here too. Tosaf. reverses the premise and the conclusion.');"><sup>11</sup></span> But that is obvious? - I might have argued, But he did not say to her, 'After thirty days';<span class="x" onmousemove="('comment',' Rashi: Her master did not state that he would designate her after a certain period, therefore the second man's betrothal is valid. But if one says: 'Be betrothed to me after thirty days,' I might have thought that she is betrothed to him, and the second man's betrothal is invalid. Tosaf.: her master did not state that he would designate her only after a certain period, and therefore I would have thought that the designation commences immediately, and the second man's betrothal is invalid.');"><sup>12</sup></span>