Exodus 6:28-30

28 ¶ And it came to pass on the day when the Lord spake unto Moses in the land of Egypt, 29 That the Lord spake unto Moses, saying, I am the Lord: speak thou unto Pharaoh king of Egypt all that I say unto thee. 30 And Moses said before the Lord, Behold, I am of uncircumcised lips, and how shall Pharaoh hearken unto me?