The angel answered her, "The Holy Spirit will come on you, and the power of the Most High will overshadow you. Therefore also the holy one who is born from you will be called the Son of God.
What prayer? For years he had been praying, "Lord, please give me a son." It really gives to us encouragement for persistence in prayer. He didn't give up. Even though he was now old. Well stricken with years. He was still praying, "Oh, Lord, I'd love to have a son."