Reference for Yevamot 42:3
אמינא אי גברא רבה הוינא אסברא מדעתי אי מקרי דרדקי הוינא אשיילה מרבנן דאתו לבי כנישתא השתא סברתה מדעתי לא אסרו כלת בתו אלא משום כלת בנו
on my own; and should I be a Scripture teacher of little children I would ask the Rabbis who come to the school house.<span class="x" onmousemove="('comment',' [Lit., 'House of Assembly', the synagogue to which was attached the school for children.] ');"><sup>7</sup></span> Now I am in a position to explain it on my own: The daughter-in-law of one's daughter was forbidden only on account of the daughter-in-law of one's son. Said Abaye to Raba: I can explain it to you: Take as an example a daughter-in-law of the house of Bar Zithai.<span class="x" onmousemove="('comment',' In that family there were both a daughter-in-law of Bar Zithai's son and a daughter-in-law of his daughter, and permission to marry the latter might easily have led to the erroneous conclusion that the former also was permitted. ');"><sup>8</sup></span>