Sahih Bukhari Volume 1, Book 10, Hadith 647

حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، قَالَ حَدَّثَنَا عَبْدُ الْوَاحِدِ، قَالَ حَدَّثَنَا الأَعْمَشُ، قَالَ سَمِعْتُ أَبَا صَالِحٍ، يَقُولُ سَمِعْتُ أَبَا هُرَيْرَةَ، يَقُولُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ صَلاَةُ الرَّجُلِ فِي الْجَمَاعَةِ تُضَعَّفُ عَلَى صَلاَتِهِ فِي بَيْتِهِ وَفِي سُوقِهِ خَمْسًا وَعِشْرِينَ ضِعْفًا، وَذَلِكَ أَنَّهُ إِذَا تَوَضَّأَ فَأَحْسَنَ الْوُضُوءَ، ثُمَّ خَرَجَ إِلَى الْمَسْجِدِ لاَ يُخْرِجُهُ إِلاَّ الصَّلاَةُ، لَمْ يَخْطُ خَطْوَةً إِلاَّ رُفِعَتْ لَهُ بِهَا دَرَجَةٌ، وَحُطَّ عَنْهُ بِهَا خَطِيئَةٌ، فَإِذَا صَلَّى لَمْ تَزَلِ الْمَلاَئِكَةُ تُصَلِّي عَلَيْهِ مَا دَامَ فِي مُصَلاَّهُ اللَّهُمَّ صَلِّ عَلَيْهِ، اللَّهُمَّ ارْحَمْهُ‏.‏ وَلاَ يَزَالُ أَحَدُكُمْ فِي صَلاَةٍ مَا انْتَظَرَ الصَّلاَةَ ‏"

Narrated By Abu Huraira : Allah's Apostle said, "The reward of the prayer offered by a person in congregation is twenty five times greater than that of the prayer offered in one's house or in the market (alone). And this is because if he performs ablution and does it perfectly and then proceeds to the mosque with the sole intention of praying, then for every step he takes towards the mosque, he is upgraded one degree in reward and his one sin is taken off (crossed out) from his accounts (of deeds). When he offers his prayer, the angels keep on asking Allah's Blessings and Allah's forgiveness for him as long as he is (staying) at his Musalla. They say, 'O Allah! Bestow Your blessings upon him, be Merciful and kind to him.' And one is regarded in prayer as long as one is waiting for the prayer."