Musannaf Ibn Abi Shayba 3:6478

Abu Bakr narrated to us, he said: Ibn ‘Ulayyah narrated to us, from Khalid, who said: I saw Abu Qilabah wearing a jubbah (outer garment), a milhafah (wrapper), and a ghasilah (a type of garment), and he was praying while lying on his side, having taken out his right hand.