Romans 4:21 in the King James Version
And being fully persuaded that, what he had promised, he was able also to perform.
Context
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 also able to perform.
22 Therefore it also was “credited to him for righteousness.”