Jamiat Tirmidhi: Hadith 145

Ibn Abbas was asked ahout Tayammum. He said: "When Allah mentioned Wudu in His Book, He said: "So wash your faces and your hands (forearms) up to the elbows." And He said about Tayammum: "And rub therewith your faces and hands" And He said: "And the male thief and the female thief; cut off their hands." So the Sunnah for cutting is the two hands. So it is only the face and the hands, meaning, Tayammum."