Hadith: .

عَنْ أَنَسِ بْنِ مَالِكٍ رَضيَ اللهُ عنه قَالَ:
بَيْنَمَا نَحْنُ فِي الْمَسْجِدِ مَعَ رَسُولِ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ إِذْ جَاءَ أَعْرَابِيٌّ، فَقَامَ يَبُولُ فِي الْمَسْجِدِ، فَقَالَ أَصْحَابُ رَسُولِ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ: مَهْ مَهْ، قَالَ: قَالَ رَسُولُ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ: «لَا تُزْرِمُوهُ، دَعُوهُ» فَتَرَكُوهُ حَتَّى بَالَ، ثُمَّ إِنَّ رَسُولَ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ دَعَاهُ فَقَالَ لَهُ: «إِنَّ هَذِهِ الْمَسَاجِدَ لَا تَصْلُحُ لِشَيْءٍ مِنْ هَذَا الْبَوْلِ، وَلَا الْقَذَرِ إِنَّمَا هِيَ لِذِكْرِ اللهِ عَزَّ وَجَلَّ، وَالصَّلَاةِ وَقِرَاءَةِ الْقُرْآنِ» أَوْ كَمَا قَالَ رَسُولُ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ قَالَ: فَأَمَرَ رَجُلًا مِنَ الْقَوْمِ فَجَاءَ بِدَلْوٍ مِنْ مَاءٍ فَشَنَّهُ عَلَيْهِ.
[صحيح] - [متفق عليه] - [صحيح مسلم: 285]

Anas ibn Mālik (may Allah be pleased with him) reported:
While we were in the mosque with the Messenger of Allah (may Allah's peace and blessings be upon him), a Bedouin came and began to urinate in the mosque. The Companions of the Messenger of Allah (may Allah's peace and blessings be upon him) said: Stop! Stop! He said: The Messenger of Allah (may Allah's peace and blessings be upon him) said: "Do not interrupt him; let him." So they left him until he finished urinating. Then the Messenger of Allah (may Allah's peace and blessings be upon him) called him and said to him: "These mosques are not appropriate for anything of this kind of urine or filth. They are only for the remembrance of Allah Almighty, prayer, and recitation of the Qur’an" or as the Messenger of Allah (may Allah's peace and blessings be upon him) said. He said: Then he ordered a man from among the people who brought a bucket of water and poured it over the affected area.
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Muslim - 285]

Explanation

The Prophet (may Allah's peace and blessings be upon him) was in his mosque with his Companions when a Bedouin from the desert came and began to urinate in a corner of the mosque. The Companions rebuked him and said: Stop! Hold yourself back from that! The Prophet (may Allah's peace and blessings be upon him) said: Leave him alone, and do not interrupt his urination. So they left him until he finished.
Then he (may Allah's peace and blessings be upon him) called him and said to him: Indeed, mosques are not suitable for anything of this urine or any kind of filth. They are only for the remembrance of Allah Almighty, prayer, the recitation of the Qur’an, and the like. Then the Prophet (may Allah's peace and blessings be upon him) instructed one of the Companions, who brought a bucket full of water and gently poured it over his urine.

Benefits from the Hadith

1. It is obligatory to honor mosques and protect them from anything inappropriate.
2. An-Nawawi said: This indicates the importance of maintaining and revering mosques and keeping them free from filth, dirt, and spitting, as well as from loud voices, disputes, buying and selling, and all other types of transactions or anything similar to them.
3. Gentleness with the ignorant and teaching them what they need to know should be done without harshness or harm, so long as their mistake was not made out of contempt or stubbornness.
4. The Prophet (may Allah's peace and blessings be upon him) was a compassionate instructor, a gentle discipliner, and a tolerant educator.
5. Encouragement to maintain and enliven the houses of Allah Almighty through prayer, recitation of the Qur’an, and remembrance of Allah Almighty.