Compare Jonah 3:5, 10 with Ephesians 2:8-10 KJB

Jonah 3:5 KJB
[5] So the people of Nineveh believed God, and proclaimed a fast, and put on sackcloth, from the greatest of them even to the least of them.
[10] And God saw their works, that they turned from their evil way; and God repented of the evil, that he had said that he would do unto them; and he did it not.

Ephesians 2:8-10 KJB
[8] For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: [9] not of works, lest any man should boast.
[10] For we are his workmanship, created in Christ Jesus unto good works, which God hath before ordained that we should walk in them.

Turn from evil ways/turn from sin IS works (Jonah 3:10).
Works do not save us; we are not saved by works (Ephesians 2:8-10). Thus, turning from sin/repenting of sins is works and does not save us.

Repentance Examined