Sahih Bukhari: Volume 1, Book 8, Number 441:

Narrated 'Ubdaidullah Al-Khaulani:

I heard 'Uthman bin 'Affan saying, when people argued too much about his intention to reconstruct the mosque of Allah's Apostle, "You have talked too much. I heard the Prophet saying, 'Whoever built a mosque, (Bukair thought that 'Asim, another subnarrator, added, "Intending Allah's Pleasure"), Allah would build for him a similar place in Paradise.' "