Abraham believed the Lord, and it was credited to him as righteousness. Genesis 15:6

Without weakening in his faith, Abraham acknowledged the decrepitness of his body since he was about a hundred years old and the lifelessness of Sarah’s womb. Yet, he did not waver through disbelief in the promise of God, but was strengthened in his faith and gave glory to God, being fully persuaded that God was able to do what He had promised Romans 4:19-21