It was narrated from Mu’adhah Al-‘Adawiyyah that ‘Aishah said:
“The Messenger of Allah ﷺ used to fast three days of each month.” I said: “Which were they?” She said: “He did not care which days they were.”

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا غُنْدَرٌ، عَنْ شُعْبَةَ، عَنْ يَزِيدَ الرِّشْكِ، عَنْ مُعَاذَةَ الْعَدَوِيَّةِ، عَنْ عَائِشَةَ، أَنَّهَا قَالَتْ كَانَ رَسُولُ اللَّهِ ـ ﷺ ـ يَصُومُ ثَلاَثَةَ أَيَّامٍ مِنْ كُلِّ شَهْرٍ . قُلْتُ مِنْ أَيِّهِ قَالَتْ لَمْ يَكُنْ يُبَالِي مِنْ أَيِّهِ كَانَ .