He considered his own body to be already dead (since he was about a hundred years old), and the deadness of Sarah's womb, without weakening in the faith.
References for Romans 4:19
He did not waver in unbelief at God's promise, but was strengthened in his faith and gave glory to God,
because he was fully convinced that what He had promised He was also able to perform.
Therefore, it was credited to him for righteousness.
References for Romans 4:22
Now it was credited to him was not written for Abraham alone,
but also for us. It will be credited to us who believe in Him who raised Jesus our Lord from the dead.
He was delivered up for our trespasses and raised for our justification.
References for Romans 4:25