Shaykh Abdul Sattar al-Hammad
Hadith Commentary:
In the narration of Anas (radi Allahu anhu), phlegm is mentioned; in the hadith narrated from Ibn Umar (radi Allahu anhu), saliva is mentioned; and in the narration of Aisha (radi Allahu anha), due to doubt, nasal mucus, saliva, and phlegm are all mentioned.
Imam Bukhari (rahimahullah), by bringing these three narrations together, intends to show that whether it is saliva from the mouth, mucus from the nose, or phlegm from the chest, all three are repulsive substances, and in the matter of the mosque, their ruling is the same.
If these things are seen on the floor of the mosque or on the qiblah wall, whether they are wet or dry, out of respect for the mosque it is necessary that they be removed immediately. This is the responsibility of every person who sees them; one should not wait for the mosque's caretaker or the muezzin.
These things also cause discomfort to the worshippers, therefore, under no circumstances should they be left as they are.
Source: Hidayat al-Qari: Commentary on Sahih Bukhari, Urdu, Page: 407