Exodus 4:10
9 And if they do not believe even these two signs or listen to you, then take some water from the Nile and pour it out on the dry ground. The water you take out of the Nile will become blood on the dry ground.” 10 Then Moses said to the Lord, “O my Lord, I am not an eloquent man, neither in the past nor since you have spoken to your servant, for I am slow of speech and slow of tongue.” 11 The Lord said to him, “Who gave a mouth to man, or who makes a person mute or deaf or seeing or blind? Is it not I, the Lord?
Acts 7:22
20 At that time Moses was born, and he was beautiful to God. For three months he was brought up in his father’s house, 21 and when he had been abandoned, Pharaoh’s daughter adopted him and brought him up as her own son. 22 So Moses was trained in all the wisdom of the Egyptians and was powerful in his words and deeds. 23 But when he was about forty years old, it entered his mind to visit his fellow countrymen the Israelites.
Notes and References
"... Cast into the Nile, Moses ended up being saved by Pharaoh's daughter, who raised him as her own. The Bible says nothing, however, of the education that Moses received in Pharaoh's court ... To make matters worse, when God later tells Moses to go to Pharaoh in order to argue his people's cause, Moses replies, "Oh my Lord, I am not a man of words ... but I am heavy of speech and heavy of tongue" (Exodus 4:10). Eloquence, in the ancient world, was thought to be largely the result of schooling - and it was one of the most important things a person could possess ... the idea that Moses had not received a thorough education was certainly contradicted by the eloquent words he spoke throughout the Bible - and in particular by the book of Deuteronomy, which is, almost from beginning to end, one long, highly eloquent speech uttered by Moses just before his death. For all such reasons, then, ancient interpreters were quick to supply what the book of Exodus had omitted, some account of Moses' schooling ..."
Kugel, James L. The Bible as it Was (pp. 295-296) Harvard University Press, 1998