(71) باب مَنْ قَالَ لاَ يُبَالِي مِنْ أَىِّ الشَّهْرِ
Mu'adhah (al-'Adawiyyah) said:
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.
Reference: Sunan Abi Dawud 2453
In-book reference: Book 14, Hadith 141
English translation: Book 13, Hadith 2447