Thematic Bible: Her miraculous conception of isaac

And God said unto Abraham, "Sarai, thy wife, shall no more be called Sarai: but Sara shall her name be. For I will bless her and give thee a son of her; and will bless her so that people, yea and kings of people, shall spring of her." And Abraham fell upon his face and laughed, and said in his heart, "Shall a child be born unto him that is a hundred years old? And shall Sara, that is ninety years old, bear?" read more.
And Abraham said unto God, "O that Ishmael might live in thy sight!" Then said God, "Nay. Sara thy wife shall bear thee a son, and thou shalt call his name Isaac. And I will make my covenant with him, that it shall be an everlasting covenant unto his seed after him. And as concerning Ishmael also, I have heard thy request: lo, I will bless him and increase him, and multiply him exceedingly. Twelve princes shall he beget, and I will make a great nation of him. But my covenant will I make with Isaac, which Sara shall bear unto thee: even this time, twelve month."

And they said unto him, "Where is Sara, thy wife?" And he said, "In the tent." And he said, "I will come again unto thee as soon as the fruit can live. And lo, Sara thy wife shall have a son." That heard Sara, out of the tent door which was behind his back. Abraham and Sara were both old and well stricken in age, and it ceased to be with Sara after the manner as it is with wives. read more.
And Sara laughed in herself saying, "Now I am waxed old, shall I give myself to lust, and my lord old also?" Then said the LORD unto Abraham, "Wherefore doth Sara laugh saying, 'shall I of a surety bear a child, now when I am old?' Is the thing too hard for the LORD to do? In the time appointed will I return unto thee, as soon as the fruit can have life. And Sara shall have a son." Then Sara denied it, saying, "I laughed not." For she was afraid. But he said, "Yes, thou laughtest."