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." (Using translation from Ibn Mājah 738)
مَنْ بَنَى لِلَّهِ ﷻ مَسْجِدًا وَلَوْ مَفْحَصَ قَطَاةٍ بَنَى اللهُ لَهُ بَيْتًا فِي الْجَنَّةِ