Sunan an-Nasa'i, Book 1, Hadith 240 (In-Book) ⓘ

It was narrated that Humaid bin 'Abdur-Rahman said: "I met a man who accompanied the Prophet as Abu Hurairah (may Allah be pleased with him), accompanied him for four years. He said: 'The Messenger of Allah 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.

أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ دَاوُدَ الأَوْدِيِّ، عَنْ حُمَيْدِ بْنِ عَبْدِ الرَّحْمَنِ، قَالَ لَقِيتُ رَجُلاً صَحِبَ النَّبِيَّ صلى الله عليه وسلم كَمَا صَحِبَهُ أَبُو هُرَيْرَةَ - رضى الله عنه - أَرْبَعَ سِنِينَ قَالَ نَهَى رَسُولُ اللَّهِ صلى الله عليه وسلم أَنْ يَمْتَشِطَ أَحَدُنَا كُلَّ يَوْمٍ أَوْ يَبُولَ فِي مُغْتَسَلِهِ أَوْ يَغْتَسِلَ الرَّجُلُ بِفَضْلِ الْمَرْأَةِ وَالْمَرْأَةُ بِفَضْلِ الرَّجُلِ وَلْيَغْتَرِفَا جَمِيعًا ‏.‏