Romans 4:18-21

18 Who in hope believed against hope, to the end that he might become a father of many nations, according to that which had been spoken, "So will your seed be."  19 Without being weakened in faith, he didn't consider his own body, already having been worn out, (he being about a hundred years old), and the deadness of Sarah's womb.  20 Yet, looking to the promise of God, he didn't waver through unbelief, but grew strong through faith, giving glory to God,  21 and being fully assured that what he had promised, he was able also to perform.