Under what circumstances was it credited? Was it after he was circumcised, or before? It was not after, but before!
And he received circumcision as a sign, a seal of the righteousness that he had by faith while he was still uncircumcised. So then, he is the father of all who believe but have not been circumcised, in order that righteousness might be credited to them.
References for Romans 4:11
And he is then also the father of the circumcised who not only are circumcised but who also follow in the footsteps of the faith that our father Abraham had before he was circumcised.
It was not through the law that Abraham and his offspring received the promise that he would be heir of the world, but through the righteousness that comes by faith.
References for Romans 4:13
For if those who depend on the law are heirs, faith means nothing and the promise is worthless,
References for Romans 4:14
because the law brings wrath. And where there is no law there is no transgression.
References for Romans 4:15
Therefore, the promise comes by faith, so that it may be by grace and may be guaranteed to all Abraham’s offspring—not only to those who are of the law but also to those who have the faith of Abraham. He is the father of us all.
References for Romans 4:16
As it is written: “I have made you a father of many nations.” He is our father in the sight of God, in whom he believed—the God who gives life to the dead and calls into being things that were not.
References for Romans 4:17
Against all hope, Abraham in hope believed and so became the father of many nations, just as it had been said to him, “So shall your offspring be.”
References for Romans 4:18
Without weakening in his faith, he faced the fact that his body was as good as dead—since he was about a hundred years old—and that Sarah’s womb was also dead.
References for Romans 4:19
Yet he did not waver through unbelief regarding the promise of God, but was strengthened in his faith and gave glory to God,
References for Romans 4:20