Joshua 9:18-20

18But the Israelites did not attack the towns, for the Israelite leaders had made a vow to them in the name of the Lord, the God of Israel. The people of Israel grumbled against their leaders because of the treaty.

19But the leaders replied, “Since we have sworn an oath in the presence of the Lord, the God of Israel, we cannot touch them.

20This is what we must do. We must let them live, for divine anger would come upon us if we broke our oath.