Romans 4:16-21

Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all, (as it is written, I have made thee a father of many nations,) before him whom he believed, even God, who quickeneth the dead, and calleth those things which be not as though they were. Who against hope believed in hope, that he might become the father of many nations, according to that which was spoken, So shall thy seed be. And being not weak in faith, he considered not his own body now dead, when he was about an hundred years old, neither yet the deadness of Sarah's womb: he staggered not at the promise of God through unbelief; but was strong in faith, giving glory to God; and being fully persuaded that, what he had promised, he was able also to perform.