Exodus 4:22
Then tell Pharaoh that this is what the LORD says: 'Israel is My firstborn son,

Exodus 4:23
and I told you to let My son go so that he may worship Me. But you have refused to let him go, so I will kill your firstborn son!'"

Exodus 5:1
Afterward, Moses and Aaron went to Pharaoh and said, "This is what the LORD, the God of Israel, says: 'Let My people go, so that they may hold a feast to Me in the wilderness.'"

Exodus 6:10
So the LORD said to Moses,

Exodus 6:29
He said to him, "I am the LORD; tell Pharaoh king of Egypt everything that I say to you."