Sunan Ibn Majah 738
سنن ابن ماجه#738SahihIt was narrated from Jabir bin 'Abdullah that: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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 4:4