Musannaf Ibn Abi Shayba 1:1450

Abu Bakr narrated to us, he said: Ibn ‘Ulayyah narrated to us, from ‘Ubayd Allah ibn al-‘Ayzār, from Ṭalq ibn Ḥabīb, who said: ‘Umar ibn al-Khaṭṭāb saw a man scratching his armpit or touching it, so he said to him: "Stand up and wash your hand, or purify yourself."