Genesis 21:1-8

Then the Lord visited Sarah, just as he had promised; and he fulfilled what he had spoken. And she conceived and gave birth to a son in her old age, at the time that God had foretold to her. And Abraham called the name of his son, whom Sarah bore for him, Isaac. And he circumcised him on the eighth day, just as God had instructed him, when he was one hundred years old. Indeed, at this stage of his father's life, Isaac was born. And Sarah said: "God has brought laughter to me. Whoever will hear of it will laugh with me." And again, she said: "Hearing this, who would believe Abraham, that Sarah breast-fed a son, to whom she gave birth, despite being elderly?" And the boy grew and was weaned. And Abraham made a great feast on the day of his weaning.