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 ‏.‏

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, 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.'"
It is said this is to prevent him from making his physical appearance his main aim.