Cleaning the mosque

There is no report of any specific virtue attached to
cleaning the mosque, except that the Prophet (peace and blessings of
Allaah be upon him) commanded that the mosque should be cleaned and
perfumed. It was narrated that Samurah ibn Jundub said: “The Messenger of
Allaah (peace and blessings of Allaah be upon him) commanded us to set
up mosques among our houses and commanded us to clean them.” (Narrated by
Ahmad in his Musnad, 19671; classed as saheeh by al-Albaani in
Saheeh al-Targheeb wa’l-Tarheeb, 278). 

And it was narrated that ‘Aa’ishah said: “The Messenger of
Allaah (peace and blessings of Allaah be upon him) commanded that
mosques should be built among the houses (i.e., in each neighbourhood), and
that they should be cleaned and perfumed.” (narrated by al-Tirmidhi, 594;
classed as saheeh by al-Albaani in Saheeh al-Targheeb wa’l-Tarheeb,
279). 

These two ahaadeeth refer
to the command of the Prophet (peace and blessings of Allaah be upon
him), and the one who obeys the command of the Prophet (peace and
blessings of Allaah be upon him) will be rewarded. 

It was narrated from Abu Hurayrah that a black man (or a
black woman) used to clean the mosque, and he died. The Prophet (peace
and blessings of Allaah be upon him) asked about him, and they said that he
had died. He said, “Why did you not tell me? Show me his grave.” (Or he
said, “her grave.”) So he went to her grave and offered the funeral prayer
for her. (Narrated by al-Bukhaari, 458; Muslim, 956). 

Ibn Hajar said in Fath al-Baari, “The hadeeth
indicates the virtue of cleaning the mosque, enquiring after servants and
after friends if they are absent.” 

Moreover, for the Muslim to do an act of worship or obedience
it is sufficient for him to know that this is the command of Allaah and His
Messenger. This is a sign of complete submission to the teachings of Islam,
but there is nothing wrong with asking about the reason behind it or the
reward for it, in order to feel more content with doing it. 

Note: there is a da’eef (weak) hadeeth about the virtue of
cleaning the mosque, which says, “Sweeping the mosque is the dowry of al-hoor
al-‘iyn.” (al-Silsilah al-Da’eefah, 4147), The saheeh reports
narrated above are sufficient. And Allaah knows best.