Musnad Ahmad 453:2

Yunus and ‘Affan narrated to us, they said: Abu ‘Awanah narrated to us, from Dawud ibn ‘Abdullah al-Awdi, from Humayd ibn ‘Abd al-Rahman al-Himyari, who said: I met a man who had accompanied the Prophet, may Allah bless him and grant him peace, for four years, just as Abu Hurayrah had accompanied him for four years. He said: "The Messenger of Allah, may Allah bless him and grant him peace, forbade us that any one of us should comb his hair every day, that he should urinate in his place of bathing, that a woman should bathe with the leftover water of a man, and that a man should bathe with the leftover water of a woman; rather, they should scoop [the water] together."