Uthman ibn Affan reported: The Messenger of Allah, peace and blessings be upon him, said, “No Muslim attends a prescribed prayer and performs its ablution, reverence, and bowing in the best manner, but that it will be an expiation for his previous sins as long as he did not commit a major sin, and this applies at all times.”
Source: Ṣaḥīḥ Muslim 228
Grade: Sahih (authentic) according to Muslim
عَنْ عُثْمَانَ بْنِ عَفَّانَ قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مَا مِنْ امْرِئٍ مُسْلِمٍ تَحْضُرُهُ صَلَاةٌ مَكْتُوبَةٌ فَيُحْسِنُ وُضُوءَهَا وَخُشُوعَهَا وَرُكُوعَهَا إِلَّا كَانَتْ كَفَّارَةً لِمَا قَبْلَهَا مِنْ الذُّنُوبِ مَا لَمْ يُؤْتِ كَبِيرَةً وَذَلِكَ الدَّهْرَ كُلَّهُ
228 صحيح مسلم كتاب الطهارة باب فضل الوضوء والصلاة عقبه
