Romans 4:18-19

In hope against hope Abraham believed that he would become a father of many nations, as he had been promised [by God]: “SO [numberless] SHALL YOUR DESCENDANTS BE.” [Gen 15:5] 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]