'Uthman b. 'Affan listened to the opinion of the people (which was not favourable) when he rebuilt the mosque of the Messenger of Allah (ﷺ). Thereupon he said: You have not been fair to me for I have heard from the Messenger of Allah (ﷺ) saying: He who built a mosque for Allah, the Exalted, Allah would build for him a house in Paradise. Bukair said: I think he (the Holy Prophet) said: While he seeks the pleasure of Allah (by building the mosque). And in the narration of Ibn 'Isa (the words are):" (a house) like that (mosque) in Paradise."
The Book of Mosques and Places of Prayer
Sahih Muslim - Hadith Reference: Sahih Muslim 533a
Hadith Commentary
This narration from 'Uthman ibn 'Affan demonstrates the virtue of constructing mosques for the sake of Allah alone. When the people criticized his expansion of the Prophet's Mosque, 'Uthman responded with this Prophetic tradition to clarify his sincere intention.
The phrase "Allah would build for him a house in Paradise" indicates the immense reward for this noble deed. The additional clarification "while he seeks the pleasure of Allah" emphasizes that the reward is contingent upon purity of intention, free from worldly motives such as showing off or seeking fame.
The variant narration mentioning "a house like that mosque in Paradise" suggests the heavenly abode will correspond in excellence to the mosque built on earth. This shows Allah's boundless generosity, rewarding a temporary worldly deed with an eternal, magnificent recompense.
This hadith encourages Muslims to participate in mosque construction and maintenance, while reminding them to purify their intentions solely for Allah's pleasure, following the example of the righteous caliph 'Uthman.