Exodus 6:10-12
10 And the LORD spake unto Moses, saying,
11 Go in, speak unto Pharaoh king of Egypt, that he let the children of Israel go out of his land.
12 And Moses spake before the LORD, saying, Behold, the children of Israel have not hearkened unto me; how then shall Pharaoh hear me, who am of uncircumcised lips?