Reference for Yevamot 200:14
בשלמא לשני לא ליטמי ליה אלא לראשון ליטמי ליה ממה נפשך אי בריה הוא שפיר קא מטמא ליה ואי בר בתרא הוא שפיר קא מטמא ליה דחלל הוא
R. Papa demurred: If that is so in the case of Abraham where it is written, To be a God to thee and to thy seed after thee,<span class="x" onmousemove="('comment',' Gen. XVII, 7. ');"><sup>42</sup></span> what does the All Merciful exhort him thereby!<span class="x" onmousemove="('comment',' By the expression. Thy seed after thee, which is analogous to that of Num. XXV, 23. but, referring to Israelites and not to priests. could not bear the same exposition, ');"><sup>43</sup></span> — It is this that he said to him: Marry not an idolatress or a bondwoman so that your seed shall not be ascribed to her.<span class="x" onmousemove="('comment',' The child of any such woman is ascribed to his mother and not to his father. Cf. Kid. 68b. ');"><sup>44</sup></span> An objection was raised: The first<span class="x" onmousemove="('comment',' Child born from a levirate marriage that took place within three months after the death of the deceased brother, when it is doubtful whether the child is the offspring of the deceased or of the levir. ');"><sup>45</sup></span>