Abdullah al-Khaulani reported that when Uthman b. 'Affan tried to rebuild the mosque of Allaah's Messenger (sallAllaahu alayhi wa sallam) the people began to talk about this. Uthman b. 'Affan said: You discuss it very much whereas I have heard Allaah's Messenger (sallAllaahu alayhi wa sallam) as saying: He who builds a mosque-- and the narrator Bukair said: I think he also said: (for) seeking the pleasure of Allaah- Allaah would build (a similar house for him in Paradise). and in the narration of Harun (the words are):" A house for him in Paradise."
Mahmud b. Labid reported that 'Uthman b. 'Affan decided to rebuild the mosque (of Allaah's Prophet in Medina) but the people did not like this idea and they wished that it should be preserved in the same (old) form. Thereupon he (Hadrat 'Uthman) said: I heard Allaah's Messenger (sallAllaahu alayhi wa sallam) as saying: He who builds a mosque for Allaah, Allaah would build for him (a house) in Paradise like it.
This hadith has been narrated on the authority of Ja'far with the same chain of transmitters with this variation (that the words are):" Allaah would build for him a house in Paradise."