Reference for Bekhorot 97:25

<big><strong>מתני׳</strong></big> מת האב בתוך שלשים בחזקת שלא נפדה עד שיביא ראיה שנפדה

the verses do serve as an illustration and consequently he [R'Akiba] is in doubt.<span class="x" onmousemove="('comment',' And owing to this doubt he says that if the father gave the redemption money, he cannot recover it, but that if he had not given it, he need not give it.');">²³</span>

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