Sahih Bukhari Volume 7, Book 77, Hadith 5861

حَدَّثَنَا مُحَمَّدُ بْنُ عَرْعَرَةَ، قَالَ حَدَّثَنِي عُمَرُ بْنُ أَبِي زَائِدَةَ، عَنْ عَوْنِ بْنِ أَبِي جُحَيْفَةَ، عَنْ أَبِيهِ، قَالَ أَتَيْتُ النَّبِيَّ صلى الله عليه وسلم وَهْوَ فِي قُبَّةٍ حَمْرَاءَ مِنْ أَدَمٍ، وَرَأَيْتُ بِلاَلاً أَخَذَ وَضُوءَ النَّبِيِّ صلى الله عليه وسلم وَالنَّاسُ يَبْتَدِرُونَ الْوَضُوءَ، فَمَنْ أَصَابَ مِنْهُ شَيْئًا تَمَسَّحَ بِهِ، وَمَنْ لَمْ يُصِبْ مِنْهُ شَيْئًا أَخَذَ مِنْ بَلَلِ يَدِ صَاحِبِهِ‏.‏

Narrated By Abu Juhaifa : I came to the Prophet while he was inside a red leather tent, and I saw Bilal taking the remaining water of the ablution of the Prophet, and the people were taking of that water and rubbing it on their faces; and whoever could not get anything of it, would share the moisture of the hand of his companion (and then rub it on his face).