Musnad Ahmad 559:3

Abdullah said: I found in my father’s book, in his own handwriting: Ya’la ibn ‘Ubayd narrated to us, he said: Sufyan narrated to us, from Mansur, from Mujahid, from al-Hakam ibn Sufyan—or Sufyan ibn al-Hakam—who said: "I saw the Messenger of Allah (may Allah bless him and grant him peace) urinate—meaning—then he performed ablution, then he sprinkled water over his private part."