Musannaf Ibn Abi Shayba 1:2094

Waki’ narrated to us, he said: ‘Umar ibn Dharr narrated to us, from ‘Abd al-Malik ibn al-Harith, he said: I invited Ibrahim al-Nakha’i and Ibrahim al-Taymi. They entered the privy while wearing their leather socks (khuffayn). Then they came out and performed ablution (wudu) and wiped over their leather socks, then they prayed.