Sayyiduna Abu al-Samh (may Allah be pleased with him) said: I used to serve the Prophet (peace and blessings be upon him). When he (peace and blessings be upon him) intended to take a bath, he would say: "Turn away from me." So I would turn my back towards him (peace and blessings be upon him). Once Sayyiduna Hasan or Husayn (may Allah be pleased with them both) was brought, and he urinated on his (peace and blessings be upon him) chest. I came to wash it, and he (peace and blessings be upon him) said: "The urine of a girl is washed, and water is sprinkled over the urine of a boy."
Hadith Referenceالمعجم الكبير للطبراني / مسند من يعرف بالكنى / 19161