207 – Anas (may Allah be pleased with him) reported that the Messenger of Allah (peace and blessings be upon him) said, “Spitting in the mosque is a sin, and its expiation is to bury it.” Agreed upon (1).

Vocabulary of the ḥadīth
• al-busāq: pronounced with ḍamma on the bāʾ. It has three accepted forms—buzāq (with zāʾ), buṣāq (with ṣād), and busāq (with sīn); the first two are more common. It denotes the fluid that leaves the mouth, whereas while still inside it is called saliva (rayq).
• khaṭīʾa: on the pattern faʿīla, written with a hamzah, though the hamzah may permissibly be changed to a yāʾ. It means “sin.”

Points derived from the ḥadīth
1 – Spitting—and likewise blowing one’s nose—in a mosque is among the sins, because anyone who does so is showing disrespect for the mosque. Allah, Exalted is He, says: “Whoever honors the sacred ordinances of Allah—it is best for him in the sight of his Lord” (al-Ḥajj 22:30).
2 – At first glance this narration seems to contradict the earlier report from Anas found in the two Ṣaḥīḥs: “Let him spit to his left beneath his foot.” Imām al-Nawawī reconciled them by explaining that the permission applies when one is not inside a mosque, whereas the general ruling of sinfulness remains in force when one is inside a mosque, without exception.
3 – The ḥadīth refers to spitting that occurs unintentionally; even then it is classified as a sin, though its liability is waived. Supporting this restriction is the report in al-Bukhārī 414 and Muslim 548 that the Prophet (peace and blessings be upon him) once noticed phlegm on a wall of the mosque, and it distressed him, so he scraped it off with his hand. In another wording in al-Nasāʾī (2/52): “He became so angry that his face turned red, whereupon a woman from…"