The Messenger of Allah ﷺ saw some phlegm on the qiblah wall of the mosque and scraped it off with his hand.
حدثنا عفان حدثنا حماد أخبرنا ثابت
أن رسول الله ﷺ رأى نخامة في قبلة المسجد فحكها بيده
Its chain of transmission is sahih, it has already preceded at 13501 in a fuller form than this.