Sahih Bukhari Volume 001, Book 008, Hadith Number 466.
Narated By Abu Huraira : The Prophet said, "The prayer offered in congregation is twenty five times more superior (in reward) to the prayer offered alone in one's house or in a business center, because if one performs ablution and does it perfectly, and then proceeds to the mosque with the sole intention of praying, then for each step which he takes towards the mosque, Allah upgrades him a degree in reward and (forgives) crosses out one sin till he enters the mosque. When he enters the mosque he is considered in prayer as long as he is waiting for the prayer and the angels keep on asking for Allah's forgiveness for him and they keep on saying: 'O Allah! Be Merciful to him, O Allah! Forgive him, as long as he keeps on sitting at his praying place and does not pass wind. (See Hadith No. 620).