Romans 4:17 (KJV)

And the father of circumcision to them who are not of the circumcision only, but who also walk in the steps of that faith of our father Abraham, which he had being yet uncircumcised.

For the promise, that he should be the heir of the world, was not to Abraham, or to his seed, through the law, but through the righteousness of faith.

For if they which are of the law be heirs, faith is made void, and the promise made of none effect:

Because the law worketh wrath: for where no law is, there is no transgression.

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,

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.

And therefore it was imputed to him for righteousness.