Deuteronomy 7:20

Overview - Deuteronomy 7
1	All communion with the nations is forbidden;
5	for fear of idolatry;
6	for the holiness of the people;
9	for the nature of God in his mercy and justice;
17	for the assuredness of victory which God will give over them.

Deuteronomy 7:20  (King James Version)
Moreover the LORD thy God will send the hornet among them, until they that are left, and hide themselves from thee, be destroyed.