Sunan Ibn Majah Book 1, Hadith 194
He was sitting with the Prophet who said: 'No person's prayer is complete until he performs ablution properly as Allah has commanded him, washing his face, his arms up to the elbows, wiping his head and his feet up to the ankles.'"
"I heard Humran telling Abu Burdah in the mosque that he had heard 'Uthman bin 'Affan narrating that the Prophet had said" 'Whoever performs ablution perfectly as Allah has enjoined, then his prescribed prayer will serve as expiation for what is between them."
He saw the Messenger of Allah perform ablution then take a handful of water and sprinkle it over his private area to remove any doubts about urine drippings.