Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Sa'd bin Abi Waqqas (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When any of you spits in the mosque, he should cover it so that it does not get on the body or clothes of any Muslim, for that would cause him harm."