Musnad Ahmad 559:1

Jarir narrated to us, from Mansur, from Mujahid, from Abu al-Hakam or al-Hakam ibn Sufyan al-Thaqafi, who said: "I saw the Messenger of Allah (peace and blessings of Allah be upon him) urinate, then he performed ablution, and sprinkled water over his private part." Aswad ibn Amir narrated to us, he said: Sharik said: "I asked the family of al-Hakam ibn Sufyan, and they mentioned that he did not meet the Prophet (peace and blessings of Allah be upon him)."