Sahih al-Bukhari, Hadith 219 ⓘ
Narrated Anas bin Malik: The Prophet saw a Bedouin making water in the mosque and told the people not to disturb him. When he finished, the Prophet asked for some water and poured it over (the urine).
حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، قَالَ حَدَّثَنَا هَمَّامٌ، أَخْبَرَنَا إِسْحَاقُ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم رَأَى أَعْرَابِيًّا يَبُولُ فِي الْمَسْجِدِ فَقَالَ " دَعُوهُ " . حَتَّى إِذَا فَرَغَ دَعَا بِمَاءٍ فَصَبَّهُ عَلَيْهِ.
also referenced under: Book 4, Hadith 85 (In-Book) & Volume 1, Book 4, Hadith 218 (USC-MSA)