Exodus 4:1
Then Moses answered, "What if they refuse to believe me or listen to my voice? For they may say, 'The LORD has not appeared to you.'"

Exodus 4:10
"Please, Lord," Moses replied, "I have never been eloquent, neither in the past nor since You have spoken to Your servant, for I am slow of speech and tongue."

Exodus 6:12
But in the LORD's presence Moses replied, "If the Israelites will not listen to me, then how will Pharaoh listen to me, since I am unskilled in speech?"

Isaiah 6:5
Then I said, "Woe is me, for I am ruined, because I am a man of unclean lips dwelling among a people of unclean lips, and my eyes have seen the King, the LORD of Hosts."

Jeremiah 1:6
"Ah, Lord GOD," I said, "I surely do not know how to speak, for I am only a child!"