The Messenger of Allah (sal Allahu alaihi wa sallam) said: “Whoever builds a Masjid for the sake of Allah, Allah will build something similar for him in Paradise.” [Sahih Muslim]

Uthman bin Affan (radi Allahu anhu) wanted to rebuild the Masjid of the Messenger of Allah (sal Allahu alaihi wa sallam) but people disliked it. So he told them this hadith that he had heard from the Messenger of Allah (sal Allahu alaihi wa sallam).

Building a Masjid where there isn’t one, repairing one that has fallen into disrepair, or helping to maintain one are all deeds worthy of Allah’s pleasure and the highest rewards; provided that they are done for the sake of pleasing Allah (subhana wa ta’ala) alone and not for showing off or any other purpose.

However, paying for the decoration of Masjids is not virtuous or praiseworthy. The adornment of Masjids is condemned in Ahadith, and reflects Muslims’ moving away from the real substance of Islam.