“And Peter answered him, “Lord, if it is you, command me to come to you on the water.”
He said, “Come.”
So Peter got out of the boat and walked on the water and came to Jesus.
But when he saw the wind, he was afraid, and beginning to sink he cried out, “Lord, save me.”
Jesus immediately reached out his hand and took hold of him, saying to him, “O you of little faith, why did you doubt?””
Matthew 14:28-31 ESV
http://bible.com/59/mat.14.28-31.esv