Musnad Abu Ya'la al-Mawsili 105:4

Al-Qawariri narrated to us, Sufyan narrated to us, Abu Ishaq narrated to us, from Najiyah ibn Ka'b, that 'Ammar said to 'Umar: "Do you remember when you and I were with the camels, and I became in a state of major ritual impurity (janabah)? I rolled in the dust like an animal rolls. Then I met the Prophet, peace and blessings of Allah be upon him, and I mentioned that to him. He said: 'It would have been sufficient for you to do tayammum (dry ablution) for that.'"