I was with Uthman when he called for water to perform ablution. He then said, "I heard the Messenger of Allah ﷺ say, 'There is no Muslim man who, when the time of an obligatory prayer comes, performs its ablution well and observes its humility and bowing properly, except that it will be an expiation for the sins committed before it, as long as he does not commit a major sin. And this applies for all time.'"
كنت عند عثمان فدعا بطهور فقال: سمعت رسول الله ﷺ يقول: ما من امرئ مسلم تحضره صلاة مكتوبة فيحسن وضوءها، وخشوعها، وركوعها، إلا كانت كفارة لما قبلها من الذنوب، ما لم يؤت كبيرة، وذلك الدهر كله.