Romans 4:4-5

Now when a man works, his wages are not credited to him as a gift, but as an obligation. However, to the man who does not work but trusts God who justifies the wicked, his faith is credited as righteousness.

his wages are not credited to him as a gift
Romans 11:5-6 So too, at the present time there is a remnant chosen by grace. And if by grace, then it is no longer by works; if it were, grace would no longer be grace.

his faith is credited as righteousness
Romans 4:3 What does the Scripture say? "Abraham believed God, and it was credited to him as righteousness."
Romans 4:9 Is this blessedness only for the circumcised, or also for the uncircumcised? We have been saying that Abraham's faith was credited to him as righteousness.
Romans 4:20-22 Yet he did not waver through unbelief regarding the promise of God, but was strengthened in his faith and gave glory to God, being fully persuaded that God had power to do what he had promised. This is why "it was credited to him as righteousness."
Romans 9:30 What then shall we say? That the Gentiles who did not pursue righteousness, have obtained it, a righteousness that is by faith; ...

NOTES:
Genesis 15:6

Scriptures taken from the Holy Bible, New International Version® NIV®, Copyright© 1973, 1978, 1984 by International Bible Society. Used by permission. All rights reserved worldwide.