To silence those who asked significantly, "Can one a hundred years old beget a son?" God commanded the angel who has charge over the embryos, to give them form and shape, that he fashion Isaac precisely according to the model of Abraham, so that all seeing Isaac might exclaim, "Abraham begot Isaac."
That Abraham and Sarah were blessed with offspring only after they had attained so great an age, had an important reason. It was necessary that Abraham should bear the sign of the covenant upon his body before he begot the son who was appointed to be the father of Israel. And as Isaac was the first child born to Abraham after he was marked with the sign, he did not fail to celebrate his circumcision with much pomp and ceremony on the eighth day. Shem, Eber, Abimelech king of the Philistines, and his whole retinue, Phicol the captain of his host in it--they all were present, and also Terah and his son Nahor, in a word, all the great ones round about. On this occasion Abraham could at last put a stop to the talk of the people, who said, "Look at this old couple! They picked up a foundling on the highway, and they pretend he is their own son, and to make their statement seem credible, they arrange a feast in his honor." Abraham had invited not only men to the celebration, but also the wives of the magnates with their infants, and God permitted a miracle to be done. Sarah had enough milk in her breasts to suckle all the babes there, and they who drew from her breasts had much to thank her for. Those whose mothers had harbored only pious thoughts in their minds when they let them drink the milk that flowed from the breasts of the pious Sarah, they became proselytes when they grew up; and those whose mothers let Sarah nurse them only in order to test her, they grew up to be powerful rulers, losing their dominion only at the revelation on Mount Sinai, because they would not accept the Torah. All proselytes and pious heathen are the descendants of these infants.