The Messenger of Allah ﷺ used to fast on Saturdays and Sundays more than on other days, and he would say, "They are festival days for the polytheists, and I love to differ from them."
كان رسول الله ﷺ يصوم يوم السبت ويوم الأحد أكثر مما يصوم من الأيام ويقول: إنهما يوما عيد المشركين، فأنا أحب أن أخالفهم.
Narrated by Ahmad (26750), and Tabarani in Al-Kabir (23/283). Ibn Khuzayma graded it sahih (2167), as did Ibn Hibban (3616, 3646), and Hakim (1/436). All of them narrated it through various routes from Abdullah bin Mubarak, who said, Abdullah bin Muhammad bin Umar bin Ali informed me, saying, my father narrated to us, from Kurayb, the freed slave of Ibn Abbas, from Umm Salama, and he related it.Its chain is hasan because of Abdullah bin Muhammad bin Umar bin Ali, who is the son of Abu Talib, and his father Muhammad bin Umar, for both of them are truthful narrators.