Sunan an-Nasa'i 238

It was narrated that Humaid bin 'Abdur-Rahman said:"I met a man who accompanied the Prophet (ﷺ) as Abu Hurairah (may Allah be pleased with him), accompanied him for four years. He said: 'The Messenger of Allah (ﷺ) forbade any one of us to comb his hair each day,[1] or to urinate in the place where he performs Ghusl, or for a man to perform Ghusl using the leftover water of a women, or a woman to perform Ghusl using the leftover water of a man - they should scoop it out together.'" [1] It is said this is to prevent him from making his physical appearance his main aim