رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 1694
The Book of the Prohibited actions
Prohibition of Spitting in the Mosque
وَعَنْ عَائِشَةَ رَضِيَ اللَّهُ عَنْهَا أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ رَأَى فِي جِدَارِ الْقِبْلَةِ مُخَاطًا أَوْ بزاقا أو نخامة فحكه ((مُتَّفَقٌ عَلَيْهِ)).
'Aishah (May Allah be pleased with her) said: The Messenger of Allah (ﷺ) saw spittle or snot or sputum, sticking to the wall towards Qiblah and scratched it off. [Al-Bukhari and Muslim].
Riyad as-Salihin, 1694