Romans 4:19-21

Without becoming weak in faith he considered his own body, now as good as dead [for producing children] since he was about a hundred years old, and [he considered] the deadness of Sarah’s womb. [Gen 17:17; 18:11] But he did not doubt or waver in unbelief concerning the promise of God, but he grew strong and empowered by faith, giving glory to God, being fully convinced that God had the power to do what He had promised.