Musannaf Ibn Abi Shayba 16:212

Abu Bakr narrated to us, he said: Yahya ibn Sa'id al-Qattan narrated to us, from 'Umarah ibn Mutarrif, from Yazid ibn Abi Maryam, from his father, he said: 'Umar ibn al-Khattab saw a man who had struck with his left hand to eat with it. He said: "No, unless your hand is injured or afflicted."