Chapter 5: The Book On The Mosques And The Congregations
It was narrated from Anas that: The Prophet saw some sputum in the prayer direction of the mosque and he became so angry that his face turned red. Then a woman from among the Ansar came and scraped it off, and put some Khaluq on that spot. The Messenger of Allah said: "How good this is."
Sunan Ibn Majah 762