1693/1 - Anas (may Allah be pleased with him) reported that the Prophet (may Allah’s peace and blessings be upon him) said: “Spitting in the mosque is a sin and its expiation is to bury it.” [Narrated by Al-Bukhāri and Muslim]
“To bury it” applies to the case where the floor of the mosque is dust, sand, or the like. In his book "Al-Bahr", Abu al-Mahāsin al-Rūwyāni said: “Its burial is said to mean that it should be removed from the mosque. Yet, if the mosque has a paved or slabbed floor, and a person rubs the spittle with his shoe or something else, as many ignorant people do, this is not the intended burial; on the contrary, this adds to the error and increases filth in the mosque. A person who does so should remove the spittle with his garment, hand, or something else, or wash it.
1) It is prohibited to spit in the mosque.
2) The Shariah exhorts us to remove filth from the mosque, given its inviolability and sublime status.
1694/2 - ‘Ā’ishah (may Allah be pleased with her) reported that the Messenger of Allah (may Allah’s peace and blessings be upon him) saw spittle, snot, or sputum sticking to the wall towards the Qiblah, and he scratched it off. [Narrated by Al-Bukhāri and Muslim]
1) If a person sees something dirty or impure in the mosque, he should remove it, in compliance with the Prophet’s Sunnah.
2) It urges us to extol whatever Allah has commanded to be extolled. This includes the mosques.
1695/3 - Anas (may Allah be pleased with him) reported that the Messenger of Allah (may Allah’s peace and blessings be upon him) said: “It is not appropriate to use mosques for urinating or filth. Indeed, they are built for the remembrance of Allah and the recitation of the Qur’an.” Or as the Messenger of Allah (may Allah’s peace and blessings be upon him) said it. [Narrated by Muslim]
1) A Muslim is required to show respect to mosques. He should not place any filth therein given its high status.
2) It urges filling the mosques with prayer, recitation of the Qur’an, remembrance of Allah, and beneficial knowledge classes.