The Prophet ﷺ saw some phlegm on the qiblah wall of the mosque and scraped it off with his hand.
حدثنا حسن حدثنا حماد عن ثابت
أن النبي ﷺ رأى نخامة في قبلة المسجد فحتها بيده
Its isnad is sahih, previously mentioned at 13384 and its cross-references.