Genesis 21:1-7 - The Birth Of Isaac
1 The LORD came to Sarah, just as he had said, and the LORD did for Sarah what he had promised. 2 Sarah conceived and gave birth to a son for Abraham in his old age, at the very time that God had told him. 3 Abraham named his son who was born to him Isaac the very one whom Sarah bore for him! 4 On the eighth day after his son Isaac had been born, Abraham circumcised him, just as God had commanded him. 5 Abraham was 100 years old when his son Isaac was born to him.
6 Now Sarah had said, "God has caused me to laugh, and all who hear about it will laugh with me." 7 She also said, "Who would have told Abraham that Sarah would nurse sons? Yet I have given birth to a son in my husband's old age!"