Sunan Ibn Majah, Chapter: The Chapters on Slaughtering

that the Messenger of Allah (saw) passed by a boy who was skinning a sheep. The Messenger of Allah (saw) said to him: "Step aside and I will show you how." The Messenger of Allah (saw) put his hand between the skin and the flesh, and thrust his arm in until it disappeared up to the armpit, and said: "O boy, this is how you skin it." Then he went and led the people in prayer and did not perform Wudu'.