The Messenger of Allah said: "Whoever builds a mosque for the sake of Allah, like a sparrow's nest for Allah or even smaller, Allah will build for him a house in Paradise."
أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ مَنْ بَنَى مَسْجِدًا لِلَّهِ كَمَفْحَصِ قَطَاةٍ أَوْ أَصْغَرَ بَنَى اللَّهُ لَهُ بَيْتًا فِي الْجَنَّةِ