Romans 4:21

21 being fully convinced that God was able to do what he had promised.

Romans 4:21 In-Context

19 He did not weaken in faith when he considered his own body, which was already as good as dead (for he was about a hundred years old), or when he considered the barrenness of Sarah's womb.
20 No distrust made him waver concerning the promise of God, but he grew strong in his faith as he gave glory to God,
21 being fully convinced that God was able to do what he had promised.
22 Therefore his faith "was reckoned to him as righteousness."
23 Now the words, "it was reckoned to him," were written not for his sake alone,
New Revised Standard Version Bible, copyright 1989, Division of Christian Education of the National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved.