Exodus 5:1-2

Young's Literal Translation

5 And afterwards have Moses and Aaron entered, and they say unto Pharaoh, `Thus said Jehovah, God of Israel, Send My people away, and they keep a feast to Me in the wilderness;'

² and Pharaoh saith, `Who [is] Jehovah, that I hearken to His voice, to send Israel away? I have not known Jehovah, and Israel also I do not send away.'