If we had forgotten the name of our God or extended our hands to a strange god, Would not God find this out? For He knows the secrets of the heart. (Psalm 44:20-21).
Let there be no strange god among you; Nor shall you worship any foreign god. (Psalm 81:9).
You shall not worship any other god, for YAHWEH, whose name is Jealous, is a jealous God. (Exodus 34:14).
YAHWEH our God, YAHWEH is one.... You shall fear only YAHWEH your God; and you shall worship Him and swear by His name. You shall not follow other gods, any of the gods of the peoples who surround you, for YAHWEH your God in the midst of you is a jealous God; otherwise the anger of YAHWEH your God will be kindled against you, and He will wipe you off the face of the earth. You shall not put YAHWEH your God to the test(Deuteronomy 6:4, 13-15).
Then Jesus said to him, "Begone, Satan! for it is written, 'You shall worship the Lord your God and him only shall you serve.'" (Matthew 4:10).
And if you forget the YAHWEH your God and go after other gods and serve them and worship them, I solemnly warn you this day that you shall surely perish. Like the nations that YAHWEH makes to perish before you, so you shall perish; because you would not listen to the voice of the LORD your God. (Deuteronomy 8:19-20).
Beware that your hearts are not deceived, and that you do not turn away and serve other gods and worship them. (Deuteronomy 11:16).
You shall not do so toward YAHWEH your God, for every abominable act which YAHWEH hates they have done for their gods; for they even burn their sons and daughters in the fire to their gods. Whatever I command you, you shall be careful to do; you shall not add to nor take away from it. (Deuteronomy 12:31-32).