A friend submitted the following information about Moses' speech, 
which is to be found in The Book of Exodus. Using the King James 
"Revised Standard" version, she relates, " The relevant parts begin 
when God appears to him as a burning bush. Moses tried to reject 
God's commission to become leader of the Israelites. Aaron, Moses' 
brother, was a kind of priest, called a Levite.

        But Moses said to the Lord, "Oh, my Lord, I am not eloquent,
either heretofore or since thou hast spoken to thy servant; but I am 
slow of speech and of tongue. Then the Lord said to him, "Who has 
made man's mouth? Who makes him dumb, or deaf, or seeing, or
blind? Is it not I, the Lord? Now therefore go, and I will be with 
your mouth and teach you what you shall speak." But he said, "Oh, 
my Lord, send, I pray, some other person." Then the anger of the 
Lord was kindled against Moses and he said, "Is there not Aaron, 
your brother, the Levite? I know that he can speak well, and behold, 
he is coming out to meet you, and when he sees you he will be glad 
in his heart. And you shall speak to him and put the words in his 
mouth; and I will be with your mouth and with his mouth and will 
teach you what you shall do. He shall speak for you to the people 
and  he shall be a mouth for you and you shall be to him as God..."

[The people accepted Moses and Aaron as their leaders, but efforts 
to get the Israelites released meet with failure. The Egyptians laid 
heavier and heavier burdens on the Israelites, who became very 
angry at Moses. Moses returned to the desert to confer with God, who 
instructed him to go to the Pharaoh again and ask for the Israelites' 
release.]

        But Moses said to the Lord, "Behold, the people of Israel have 
not listened to me; how then shall the Pharaoh listen to me, who am a 
man of uncircumcised lips?... On the day when the Lord spoke to Moses 
in the land of Egypt, the Lord said to Moses, "I am the Lord; tell 
Pharaoh king of Egypt all that I say to you." But Moses said to the 
Lord, " Behold, I am of uncircumcised lips; how then shall the Pharaoh 
listen to me?" And the Lord said to Moses, "See, I make you as God to 
the Pharaoh; and Aaron your brother shall be your prophet. You shall 
speak all that I command you; and Aaron your brother shall tell Pharaoh 
to let the people of Israel go out of his land."