I asked 'Aishah: Would the Messenger of Allah ﷺ fast three days every month ? She replied: Yes. I asked: Which days in the month he used to fast ? She replied: He did not care which days of the month he fasted.  

قُلْتُ لِعَائِشَةَ أَكَانَ رَسُولُ اللَّهِ ﷺ يَصُومُ مِنْ كُلِّ شَهْرٍ ثَلاَثَةَ أَيَّامٍ قَالَتْ نَعَمْ قُلْتُ مِنْ أَىِّ شَهْرٍ كَانَ يَصُومُ قَالَتْ مَا كَانَ يُبَالِي مِنْ أَىِّ أَيَّامِ الشَّهْرِ كَانَ يَصُومُ  

"I heard Mu'adhah saying to Aishah: 'Did the Messenger of Allah fast three days of every month?' She replied in the affirmative. So she said: 'Which of them would he fast?' She said: 'Which of them he would fast was not noticeable.'"  

قُلْتُ لِعَائِشَةَ أَكَانَ رَسُولُ اللَّهِ ﷺ يَصُومُ ثَلاَثَةَ أَيَّامٍ مِنْ كُلِّ شَهْرٍ قَالَتْ نَعَمْ قُلْتُ مِنْ أَيِّهِ كَانَ يَصُومُ قَالَتْ كَانَ لاَ يُبَالِي مِنْ أَيِّهِ صَامَ  

“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.”  

أَنَّهَا قَالَتْ كَانَ رَسُولُ اللَّهِ ﷺ يَصُومُ ثَلاَثَةَ أَيَّامٍ مِنْ كُلِّ شَهْرٍ قُلْتُ مِنْ أَيِّهِ؟ قَالَتْ لَمْ يَكُنْ يُبَالِي مِنْ أَيِّهِ كَانَ  

"I heard Mu'adhah saying to Aishah: 'Did the Messenger of Allah fast three days of every month?' She replied in the affirmative. So she said: 'Which of them would he fast?' She said: 'Which of them he would fast was not noticeable.'" (Using translation from Tirmidhī 763)   

قُلْتُ لِعَائِشَةَ «أَكَانَ النَّبِيُّ ﷺ يَصُومُ مِنَ الشَّهْرِ ثَلَاثَةَ أَيَّامٍ؟ » قَالَتْ نَعَمْ قُلْتُ «مِنْ أَيِّهِ؟ » قَالَتْ لَمْ يُبَالِ مِنْ أَيِّهِ صَامَ  

“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.” (Using translation from Ibn Mājah 1709)  

«كَانَ رَسُولُ اللَّهِ ﷺ يَصُومُ ثَلَاثَةَ أَيَّامٍ مِنْ كُلِّ شَهْرٍ» قُلْتُ مِنْ أَيِّهِ؟ قَالَتْ «لَمْ يَكُنْ يُبَالِي مِنْ أَيِّهِ كَانَ»