Musannaf Ibn Abi Shaybah 699 — Ghusl for janabah

Asim bin Amr said: A delegation from the people of Iraq came to Sayyiduna Umar (may Allah be pleased with him) and asked him about the bath for janabah. He said: "You have asked me about something no one has asked me about since I asked the Messenger of Allah (peace and blessings be upon him) about it. In the bath for janabah, perform the ablution that you perform for prayer."