Anas b. Malik reported: While we were in the mosque with Messenger of Allah ﷺ, a desert Arab came and stood up and began to urinate in the mosque. The Companions of Messenger of Allah ﷺ said: Stop, stop, but the Messenger of Allah ﷺ said: Don't interrupt him;
leave him alone. They left him alone, and when he finished urinating, Messenger of Allah ﷺ called him and said to him: These mosques are not the places meant for urine and filth, but are only for the remembrance of Allah, prayer and the recitation of the Qur'an, or Allah's Messenger said something like that. He (the narrator) said that he (the Holy Prophet) then gave orders to one of the people who brought a bucket of water and poured It over.

حَدَّثَنَا زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا عُمَرُ بْنُ يُونُسَ الْحَنَفِيُّ، حَدَّثَنَا عِكْرِمَةُ بْنُ عَمَّارٍ، حَدَّثَنَا إِسْحَاقُ بْنُ أَبِي طَلْحَةَ، حَدَّثَنِي أَنَسُ بْنُ مَالِكٍ، - وَهُوَ عَمُّ إِسْحَاقَ - قَالَ بَيْنَمَا نَحْنُ فِي الْمَسْجِدِ مَعَ رَسُولِ اللَّهِ ﷺ إِذْ جَاءَ أَعْرَابِيٌّ فَقَامَ يَبُولُ فِي الْمَسْجِدِ فَقَالَ أَصْحَابُ رَسُولِ اللَّهِ ﷺ مَهْ مَهْ . قَالَ قَالَ رَسُولُ اللَّهِ ﷺ " لاَ تُزْرِمُوهُ دَعُوهُ " . فَتَرَكُوهُ حَتَّى بَالَ . ثُمَّ إِنَّ رَسُولَ اللَّهِ ﷺ دَعَاهُ فَقَالَ لَهُ " إِنَّ هَذِهِ الْمَسَاجِدَ لاَ تَصْلُحُ لِشَىْءٍ مِنْ هَذَا الْبَوْلِ وَلاَ الْقَذَرِ إِنَّمَا هِيَ لِذِكْرِ اللَّهِ عَزَّ وَجَلَّ وَالصَّلاَةِ وَقِرَاءَةِ الْقُرْآنِ " . أَوْ كَمَا قَالَ رَسُولُ اللَّهِ ﷺ . قَالَ فَأَمَرَ رَجُلاً مِنَ الْقَوْمِ فَجَاءَ بِدَلْوٍ مِنْ مَاءٍ فَشَنَّهُ عَلَيْهِ .