Musannaf Ibn Abi Shayba 1:694

Abu al-Ahwas narrated to us, from Tariq, from Asim ibn Umar, who said: A group of people from the people of Iraq went out to Umar and asked him about the ritual bath for major impurity (janabah). He said: You have asked me about matters that no one has asked me about since I asked the Messenger of Allah, peace and blessings of Allah be upon him, other than you. As for the ritual bath for major impurity, perform your ablution (wudu) as you perform it for prayer.