Commentary for Kiddushin 57:18
תנו רבנן הוא לפדות ובנו לפדות הוא קודם לבנו רבי יהודה אומר בנו קודמו שזה מצותו על אביו וזה מצות בנו עליו
And how do we know that she is not bound to redeem herself?<span class="x" onmousemove="('comment',' Though 'among thy sons' is explicitly stated, the verse may imply that a father is bound to redeem his son only, but the daughter must redeem herself when she grows up.');"><sup>31</sup></span> - Because it is written, thou shalt redeem [tifdeh], [which may be read] thou shalt redeem thyself the one whom others are commanded to redeem, is commanded to redeem oneself: the one whom others are not commanded to redeem is not commanded to redeem oneself. And how do we know that others are not commanded to redeem her? - Because the Writ saith, 'and all the firstborn of man among thy sons shalt thou redeem':'<span class="x" onmousemove="('comment',' Ex. XXXIV, 20.');"><sup>32</sup></span>