The Messenger of Allah ﷺ said, "Whoever builds a mosque for Allah, even as small as a sandgrouse's nest or smaller, Allah will build for him a house in Paradise."
إن رسول الله ﷺ قال: من بنى خيرا، مسجدا الله كمفحص قطاة، أو أصغر، بنى الله له بيتا في الجنة.
Ibn Majah narrated it (738), he said, Yunus bin Abdul-Ala told us, he said, Abdullah bin Wahb told us, from Ibrahim bin Nushayt, from Abdullah bin Abdul-Rahman bin Abu Husayn Nawfali, from Ata bin Abu Rabah, from Jabir bin Abdullah, and he related the same. Its chain of transmission is sahih, and Ibn Khuzayma also graded it sahih (1292), and he narrated it in his Sahih from Yunus bin Abdul-Ala and Isa bin Ibrahim Ghafiqi, both of them from Ibn Wahb with the same chain, and at the beginning of the hadith he said, "Whoever digs water from which no thirsty liver drinks, whether of jinn, human, or bird, Allah will reward him for it on the Day of Resurrection."A similar report has been narrated from Abu Bakr Siddiq, and its chain includes Hakam bin Yaala. Abu Hatim said, "This is a munkar hadith, and Hakam bin Yaala is discarded in his narration and daif in his narration," Ilal (1/140).I say, he is Hakam bin Yaala bin Ata Muharibi. Ibn Adi mentioned him in Kamil (2/628), and said, "Munkar in his narration, he has strange reports," and he traced the mentioned hadith with a chain going back through Jafar Firyabi, who said, Sulayman bin Abdul-Rahman told us, he said, Hakam bin Yaala told us, he said, Muhammad bin Talha told us, from his father, from Abu Muamar, from Abu Bakr Siddiq, and he related the same. He said, "No one narrates this from Muhammad bin Talha, meaning Muhammad bin Talha bin Musarrif, other than Hakam bin Yaala." End of quote.A note, in Ilal the name has been corrupted, "Hakam bin Yaala bin Ata" was altered to "Hakam bin Yaala, from Ata."As for his saying, "like the nesting-place of a sand grouse," this refers to the spot where the bird crouches and lays its eggs. Qataah (sand grouse) is the singular of qata, a type of dove that prefers to live in the desert and makes itself a shallow nest in the ground. The comparison is meant for emphasis, for otherwise the minimum requirement for a masjid is simply that it be a place large enough for one person to pray in.