Good Manners and Form (Al-Adab)
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ عَبْدِ الْوَهَّابِ، حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ ثَابِتٍ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ أَعْرَابِيًّا، بَالَ فِي الْمَسْجِدِ، فَقَامُوا إِلَيْهِ، فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لا تُزْرِمُوهُ ". ثُمَّ دَعَا بِدَلْوٍ مِنْ مَاءٍ فَصُبَّ عَلَيْهِ.Narrated Anas bin Malik:A bedouin urinated in the mosque and the people ran to (beat) him. Allah's Messenger (ﷺ) said, "Do not interrupt his urination (i.e. let him finish)." Then the Prophet (ﷺ) asked for a tumbler of water and poured the water over the place of urine
From Sahih al-Bukhari, whose reports the scholars accept as authentic.