Exodus 6:27-30King James Version (KJV)
27 These are they which spake to Pharaoh king of Egypt, to bring out the children of Israel from Egypt: these are that Moses and Aaron.
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?