A mosque is the best of places. It is more blessed and virtuous than all other places. The Prophet (peace be upon him) said:
“The most beloved of places to Allah is the mosque, and the most detested of places to Allah is the marketplace.” [Sahîh Muslim]
There is great reward in building a mosque for Allah’s sake. The Prophet (peace be upon him) said:
“Whoever builds a mosque for Allah, Allah will build for him likewise in Paradise.” [Sahîh al-Bukhârî and Sahîh Muslim]
In some narrations of this hadith, it reads “Whoever builds a mosque seeking Allah’s pleasure…”
It is also narrated that the Prophet (peace be upon him) said:
“Whoever build a mosque for Allah – be it large or small – Allah will build for him a house in Paradise.” [Sunan al-Tirmidhî – and graded as good (hasan) by al-Albânî]
In a narration in Musnad al-Bazzâr that al-Albânî graded as authentic, it reads: “Whoever builds a mosque for Allah – though it be the size of the ground nest of a sandgrouse – Allah will build for him a house in Paradise.”
The building of a mosque is a way for a person to continue to earn blessings after death.
The Prophet (peace be upon him) said:
“Among what continues to accrue for a believer of his good works after death are the following: knowledge that he learned and then imparted to others, a pious child whom he left behind, a copy of the Qur’ân that he bequeathed, a mosque that he built, a guest house he built for travelers, a river that he made to flow, and charity he spends from his wealth when he is in good health – all of this continues to avail him after his death.” [Sunan Ibn Majah and Sunan al-Bayhaqî – and graded as good (hasan) by al-Albânî]
Al-Shawkânî comments on this hadîth in Nayl al-Awtâr (2/213), saying: “This shows that the blessings which are mentioned are for the actual construction of a mosque. It is not enough to designate land as a mosque – or to demarcate the land in some way – without building a structure on it.”
And Allah knows best.