פירוש על קידושין 142:5

R. Yehudah does not seem to want to marry off his son because he cannot determine the lineage of the women around him. Ulla begins to point out that we too do not know our lineage. Perhaps we are descended from the Babylonians who raped Israelite women during the time when the First Temple was destroyed. R. Yehuda could respond that he holds that the offspring of a non-Jew and a Jewish woman is fit. Therefore, maybe we are pure.