Sunan Abu Dawood, Chapter: Purification (Kitab Al-Taharah)

I used to serve the Prophet (peace_be_upon_him). Whenever he intended to wash himself, he would say: Turn your back towards me, So I would turn my back and hide him. (Once) Hasan or Husayn (may Allah be pleased with them) was brought to him and he passed water on his chest. I came to wash it. He said: It is only the urine of a female which should be washed; the urine of a male should be sprinkled over.