Musannaf Ibn Abi Shayba 3:796

Hafs narrated to us, from Hallam, from Mas'ud—meaning Ibn Hirash—who said: Umar led us in prayer in a garment, having nothing else on him. He said: And Mas'ud—meaning Ibn Hirash—led us in prayer in a *naqb* (a garment with a hole for the head).