Sunan an-Nasa'i, Hadith 329 ⓘ
It was narrated from Anas that a Bedouin urinated in the Masjid, and some of the people went after him, but the Messenger of Allah said: "Do not restrain him." When he had finished he called from a bucket (of water) and poured over it.
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ ثَابِتٍ، عَنْ أَنَسٍ، أَنَّ أَعْرَابِيًّا، بَالَ فِي الْمَسْجِدِ فَقَامَ إِلَيْهِ بَعْضُ الْقَوْمِ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لاَ تُزْرِمُوهُ " . فَلَمَّا فَرَغَ دَعَا بِدَلْوٍ مِنْ مَاءٍ فَصَبَّهُ عَلَيْهِ .
also referenced under: Book 2, Hadith 5 (In-Book) & Volume 1, Book 2, Hadith 330 (DarusSalam)