Musnad Abu Ya'la al-Mawsili 134:13

Isma'il ibn Ibrahim al-Wasiti narrated to us, Ishaq al-Azraq narrated to us, from Sharik—meaning from al-A'mash, from Anas, from the Prophet (peace and blessings of Allah be upon him), who said: "Whoever builds a mosque for Allah, even if it is like the nest of a sandgrouse, Allah will build a house for him in Paradise."