Musnad Ahmad 5:507

'Abdullah narrated to us, Abu Bahr 'Abd al-Wahid ibn Ghiyath al-Basri narrated to me, and Abu 'Abd al-Rahman 'Abdullah ibn 'Umar and Sufyan ibn Waki' narrated to us, and Ahmad ibn Muhammad ibn Ayyub narrated to us, they said: Abu Bakr ibn 'Ayyash narrated to us, from Abu Hasin, from Abu 'Abd al-Rahman al-Sulami, from 'Ali, that he said: I was a man who produced much prostatic fluid (madhy), and I was shy to ask the Messenger of Allah, peace and blessings of Allah be upon him, because his daughter was with me. So I ordered a man, and he asked him. He said: "From it is the ablution (wudu)."