Bulugh al-Maram, Book 5, Hadith 693 (In-Book) ⓘ

Umm Salamah (RAA) narrated, The Messenger of Allah used to fast more often on Saturdays and Sundays than on the other days. He would say, "They are the 'ids of the polytheists, and I love to act contrary to what they do." Related by An-Nasal and was rendered authentic by Ibn Khuzaimah, and the wording is his.

وَعَنْ أُمِّ سَلَمَةَ رَضِيَ اَللَّهُ عَنْهَا; { أَنَّ رَسُولَ اَللَّهِ ‏- صلى الله عليه وسلم ‏-كَانَ أَكْثَرَ مَا يَصُومُ مِنَ اَلْأَيَّامِ يَوْمُ اَلسَّبْتِ, وَيَوْمُ اَلْأَحَدِ, وَكَانَ يَقُولُ: " إِنَّهُمَا يَوْمَا عِيدٍ لِلْمُشْرِكِينَ, وَأَنَا أُرِيدُ أَنْ أُخَالِفَهُمْ " } أَخْرَجَهُ النَّسَائِيُّ, وَصَحَّحَهُ اِبْنُ خُزَيْمَةَ, وَهَذَا لَفْظُهُ 1‏.‏ ‏1 ‏- ضعيف.‏ رواه النسائي في " الكبرى " ( 2 / 146 )‏، وابن خزيمة ( 2167 )‏ وفي سنده مجهولان.‏