Sahih Muslim 233c
Sahih Muslim · Book 2: The Book of Purification · The five daily prayers, from one Jumu`ah to the next, and from one Ramadan to the next, are an expiation for whatever (sins) come in between, so long as one avoids major sins
Abu Huraira reported:
حَدَّثَنِي أَبُو الطَّاهِرِ ، وَهَارُونُ بْنُ سَعِيدٍ الأَيْلِيُّ ، قَالاَ أَخْبَرَنَا ابْنُ وَهْبٍ ، عَنْ أَبِي صَخْرٍ ، أَنَّ عُمَرَ بْنَ إِسْحَاقَ، مَوْلَى زَائِدَةَ حَدَّثَهُ عَنْ أَبِيهِ ، عَنْ أَبِي هُرَيْرَةَ ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَقُولُ " الصَّلَوَاتُ الْخَمْسُ وَالْجُمُعَةُ إِلَى الْجُمُعَةِ وَرَمَضَانُ إِلَى رَمَضَانَ مُكَفِّرَاتٌ مَا بَيْنَهُنَّ إِذَا اجْتَنَبَ الْكَبَائِرَ " .
Verily the Messenger of Allah (ﷺ) said: The five (daily) prayers and from one Friday prayer to the (next) Friday prayer, and from Ramadhan to Ramadhan are expiations for the (sins) committed in between (their intervals) provided one shuns the major sins.