Genesis 21:1-3
KJV1And the LORD visited Sarah as he had said, and the LORD did unto Sarah as he had spoken. 2For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him. 3And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac.
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.
Also in NKJV · ESV What the early church said about Genesis 21:1-3