When God saw their actions—that they had turned from their evil ways—He relented from the disaster He had threatened to bring upon them.
KJV
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.
ASV
And God saw their works, that they turned from their evil way; and God repented of the evil which he said he would do unto them; and he did it not.