Reference for Yevamot 124:7
אלא מהכא (דברי הימים א ב, כא) ואחר בא חצרון אל בת מכיר אבי גלעד ותלד לו את שגוב וכתיב (שופטים ה, יד) מני מכיר ירדו מחוקקים וכתיב (תהלים ס, ט) יהודה מחוקקי
and furthermore it is written, Judah is my lawgiver.<span class="x" onmousemove="('comment',' Ps. LX, 9. As this text implies that the lawgivers were descendants of Judah, Machir (Judges V, 14), a descendant of Manasseh, could not have been the paternal, but only the maternal ancestor of the lawgivers that descended from him. The lawgivers were thus the offspring of the union mentioned in I Chron. II, 21, between Hezron, a descendant of Judah, and a daughter of Machir. This then proves that the sons of one's daughter are also regarded as one's own sons. ');"><sup>16</sup></span> Our Mishnah<span class="x" onmousemove="('comment',' Which permits abstention from further propagation after the birth of the prescribed number of children. ');"><sup>17</sup></span> cannot represent the opinion of R. Joshua. For it was taught: R. Joshua said, If a man married in his youth, he should marry again in his old age; if he had children in his youth, he should also have children in his old age; for it said, In the morning<span class="x" onmousemove="('comment',' I.e., 'the morning of life', youth. ');"><sup>18</sup></span>