וַיַּ֤רְא הָֽאֱלֹהִים֙ אֶֽת־מַ֣עֲשֵׂיהֶ֔ם כִּי־שָׁ֖בוּ מִדַּרְכָּ֣ם הָרָעָ֑ה וַיִּנָּ֣חֶם הָאֱלֹהִ֗ים עַל־הָרָעָ֛ה אֲשֶׁר־דִּבֶּ֥ר לַעֲשׂוֹת־לָהֶ֖ם וְלֹ֥א עָשָֽׂה׃
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.
Read Jewish philosophy on Jonah 3:10: Rambam's Guide for the Perplexed, Saadia Gaon, and classical Jewish philosophical sources, free online.