Sahih Muslim Book - 13, Hadith - 2744

حَدَّثَنَا شَيْبَانُ بْنُ فَرُّوخَ حَدَّثَنَا عَبْدُ الْوَارِثِ عَنْ يَزِيدَ الرِّشْكِ قَالَ حَدَّثَتْنِى مُعَاذَةُ الْعَدَوِيَّةُ أَنَّهَا سَأَلَتْ عَائِشَةَ زَوْجَ النَّبِىِّ -صلى الله عليه وسلم- أَكَانَ رَسُولُ اللَّهِ -صلى الله عليه وسلم- يَصُومُ مِنْ كُلِّ شَهْرٍ ثَلاَثَةَ أَيَّامٍ قَالَتْ نَعَمْ. فَقُلْتُ لَهَا مِنْ أَىِّ أَيَّامِ الشَّهْرِ كَانَ يَصُومُ قَالَتْ لَمْ يَكُنْ يُبَالِى مِنْ أَىِّ أَيَّامِ الشَّهْرِ يَصُومُ.

Mu’adhah Al-‘Adawiyyah narrated that she asked ‘Aishah, the wife of the Prophet (SAW): “Did the Messenger of Allah (SAW) fasts three days of every month?” She said: “Yes.” She said to her: “Which three days did he fast?” She said: “He did not mind which days of the month he fasted.”