Exodus 5:2

5:2 And Pharaoh said, Who [is] the LORD, that I should obey his voice to let Israel go? I know not the LORD, neither will I let Israel go.

Exodus 23:21-22

23:21 Beware of him, and obey his voice, provoke him not; for he will not pardon your transgressions: for my name [is] in him. 23:22 But if thou shalt indeed obey his voice, and do all that I speak; then I will be an enemy unto thine enemies, and an adversary unto thine adversaries.