Musnad Ahmad 1039:4

Abdullah said: I found in my father’s book, in his own handwriting: Ya’la ibn ‘Ubayd narrated to us, Sufyan narrated to us, from Mansur, from Mujahid, from al-Hakam ibn Sufyan or Sufyan ibn al-Hakam: "That the Prophet, may Allah bless him and grant him peace, urinated, then sprinkled water on his private part."