Exodus 6:9-13

9And Moses spoke so to the children of Israel: but they hearkened not to Moses by reason of anguish of spirit, and cruel bondage.1

10And the LORD spoke to Moses, saying, 11Go in, speak to Pharaoh king of Egypt, that he let the children of Israel depart from his land. 12And Moses spoke before the LORD, saying, Behold, the children of Israel have not hearkened to me; how then shall Pharaoh hear me, who am of uncircumcised lips? 13And the LORD spoke to Moses and to Aaron, and gave them a charge to the children of Israel, and to Pharaoh king of Egypt, to bring the children of Israel out of the land of Egypt.