Sahih Muslim Book 42, Hadith Number 7109.

Chapter : Excellence of Building Mosques.

Abdullah al-Khaulani reported that when Uthman b. ‘Affan tried to rebuild the mosque of Allah’s Messenger (may peace be upon him) the people began to talk about this. Uthman b. ‘Affan said: You discuss it very much whereas I have heard Allah’s Messenger (may peace be upon him) as saying: He who builds a mosque and the narrator Bukair said: I think he also said: (for) seeking the pleasure of Allah, Allah would build (a similar house for him in Paradise) and in the narration of Harun (the words are): “A house for him in Paradise.”