I used to serve the Prophet ﷺ. Whenever he wanted to take a bath, he would say, "Turn your back toward me," so I would turn my back to him and screen him with it.Once Hasan or Husayn was brought to him, and the child urinated on his chest. I came to wash it, and he said, "The urine of a girl is washed, and the urine of a boy is sprinkled with water."
حدثنا مجاهد بن موسى وعباس بن عبد العظيم العنبري المعنى قالا حدثنا عبد الرحمن بن مهدي حدثني يحيى بن الوليد حدثني محل بن خليفة
كنت أخدم النبي ﷺ فكان إذا أراد أن يغتسل قال ولني قفاك فأوليه قفاي فأستره به فأتي بحسن أو حسين رضي الله عنهما فبال على صدره فجئت أغسله فقال يغسل من بول الجارية ويرش من بول الغلام
Its isnad is sahih. Nasai narrated it in Taharah, chapter on mentioning the practice of screening oneself during ghusl, 225, and Ibn Majah, 526, from Mujahid bin Musa in an abridged form. Ibn Khuzayma graded it sahih, 283, as did Hakim, 1/166, and Dhahabi agreed with him.