And Abram and Nahor took wives for themselves. Abram’s wife was named Sarai, and Nahor’s wife was named Milcah; she was the daughter of Haran, who was the father of both Milcah and Iscah. But Sarai was barren; she had no children.
Then God said to Abraham, “As for Sarai your wife, do not call her Sarai, for her name is to be Sarah. And I will bless her and will surely give you a son by her. I will bless her, and she will be the mother of nations; kings of peoples will descend from her.” Abraham fell facedown. Then he laughed and said to himself, “Can a child be born to a man who is a hundred years old? Can Sarah give birth at the age of ninety?” And Abraham said to God, “O that Ishmael might live under Your blessing!” But God replied, “Your wife Sarah will indeed bear you a son, and you are to name him Isaac. I will establish My covenant with him as an everlasting covenant for his descendants after him.
Then the LORD said, “I will surely return to you at this time next year, and your wife Sarah will have a son!” Now Sarah was behind him, listening at the entrance to the tent. And Abraham and Sarah were already old and well along in years; Sarah had passed the age of childbearing. So she laughed to herself, saying, “After I am worn out and my master is old, will I now have this pleasure?” And the LORD asked Abraham, “Why did Sarah laugh and say, ‘Can I really bear a child when I am old?’ Is anything too difficult for the LORD? At the appointed time I will return to you—in about a year—and Sarah will have a son.”
Now the LORD attended to Sarah as He had said, and the LORD did for Sarah what He had promised. So Sarah conceived and bore a son to Abraham in his old age, at the very time God had promised. And Abraham gave the name Isaac to the son Sarah bore to him. When his son Isaac was eight days old, Abraham circumcised him, as God had commanded him. Abraham was a hundred years old when his son Isaac was born to him. Then Sarah said, “God has made me laugh, and everyone who hears of this will laugh with me.” She added, “Who would have told Abraham that Sarah would nurse children? Yet I have borne him a son in his old age.”
Without weakening in his faith, he acknowledged the decrepitness of his body (since he was about a hundred years old) and the lifelessness of Sarah’s womb.