Romans 3:27-28

3:27 Where, then, is boasting? It is excluded! By what principle? Of works? No, but by the principle of faith! 3:28 For we consider that a person is declared righteous by faith apart from the works of the law.

Romans 4:4

4:4 Now to the one who works, his pay is not credited due to grace but due to obligation.

Romans 4:6

4:6 So even David himself speaks regarding the blessedness of the man to whom God credits righteousness apart from works:

Romans 11:6

11:6 And if it is by grace, it is no longer by works, otherwise grace would no longer be grace.