Romans 4:20–21

Paul says Abraham did not doubt: he was convinced God could do what he promised

20yet with respect to the promise of God he did not waver in unbelief, but was strengthened in faith, giving glory to God,

21and was fully convinced that what he had promised he was able also to do.

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In its context

18He believed, in hope against hope, so that he would become the father of many nations according to what had been said: So your offspring will be.

19And without weakening in faith, he considered his own body dead (since he was about a hundred years old), and the deadness of Sarah’s womb;

…

22That is why it was counted to him as righteousness.

23But it was not written for the sake of him alone that it was counted to him,

Read all of Romans 4

Its words in the original

Faithfulness