Hadith is about Spitting in the Masjid

Anas bin Malik RA said: The Messenger of Allah (sallallaahu ’alayhi wa sallam) said, "Spitting in the mosque is a sin, and its expiation is that the spittle should be buried in earth." (Bukhari and Muslim) Commentary: To atone for spitting in the mosque, one should bury the spittle in earth, but this applies when the floor of the mosque is covered with earth; as this is not the case today, one should wipe the spittle off or wash it off with clean water.