I was with Uthman, and he called for ablution water and said: I heard Messenger of Allah ﷺ say: When the time for a prescribed prayer comes, if any Muslim performs ablution well and offers his prayer with humility and bowing, it will be an expiation for his past sins, so long as he has not committed a major sin; and this applies for all times.
سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ مَا مِنِ امْرِئٍ مُسْلِمٍ تَحْضُرُهُ صَلاَةٌ مَكْتُوبَةٌ فَيُحْسِنُ وُضُوءَهَا وَخُشُوعَهَا وَرُكُوعَهَا إِلاَّ كَانَتْ كَفَّارَةً لِمَا قَبْلَهَا مِنَ الذُّنُوبِ مَا لَمْ يُؤْتِ كَبِيرَةً وَذَلِكَ الدَّهْرَ كُلَّهُ