‘Aishah reports that the Prophet ordered that mosques be built in residential areas and that they be cleaned and perfumed. This is related by Ahmad, Abu Dawud, at-Tirmizhi, Ibn Majah, and Ibn Hibban with a good chain. Abu Dawud’s wording is: “He ordered us to build the mosques in the residential areas, to build them well, and to purify them. ‘Abdullah would burn incense when ‘Umar would sit on the pulpit.”
Anas reports that the Prophet sallallahu alehi wasallam said: “The rewards of my ummah were placed before me, even for removing a speck of dust from the mosque.” This is related by Abu Dawud, at-Tirmizhi, and Ibn Khuzaimah who calls it sahih.