The Messenger of Allah ﷺ used to fast most often on Mondays and Thursdays. He was asked about this, and he said, "Deeds are presented every Monday and Thursday, and Allah forgives every Muslim," or "every believer, except for those who are estranged from one another. He says, 'Delay these two.'"
حدثنا أبو عاصم أخبرنا محمد بن رفاعة عن سهيل بن أبي صالح عن أبيه
أن رسول الله ﷺ كان أكثر ما يصوم الاثنين والخميس قال فقيل له قال فقال إن الأعمال تعرض كل اثنين وخميس أو كل يوم اثنين وخميس فيغفر الله لكل مسلم أو لكل مؤمن إلا المتهاجرين فيقول أخرهما
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Its isnad is sahih.Suyuti related it in Jami Saghir with this wording, "He fasted most often on Mondays and Thursdays." So he was asked about that, and he said, "Deeds are presented every Monday and Thursday, and every Muslim is forgiven except two who have severed relations with one another, for it is said, 'Postpone the two of them.'"He indicated that it is a hasan hadith.