Reference for Shabbat 291:2
ופליגא דר' אבא בר כהנא דא"ר אבא בר כהנא עד שלשה דורות לא פסקה זוהמא מאבותינו אברהם הוליד את ישמעאל יצחק הוליד את עשו יעקב הוליד י"ב שבטים שלא היה בהן שום דופי:
R. Aha son of Raba asked R. Ashi. What about proselytes? Though they were not present, their guiding stars<span class="x" onmousemove="('comment',' On mazzal v. Sanh., Sonc. ed., p. 629, n. 10. ');"><sup>3</sup></span> were present, as it is written, [Neither with you only do I make this covenant and this oath], but with him that standeth here with us this day before the Lord our God, and also with him that is not here with us this day.<span class="x" onmousemove="('comment',' Deut. XXIX, 14f. The teachings of Judaism and its spiritual ennoblement were freely meant for all mankind. ');"><sup>4</sup></span>