It wasnarrated from Mu'adhah Al-'Adawiyyah that 'Aishah said:
"TheMessenger of Allah (ﷺ) used to fast three days of each month." Isaid: "Which were they?" She said: "He did not care which daystheywere." (FR)
English reference (FR): Vol. 1, Book 7, Hadith 1709 (FR)
Arabic reference (FR): Book 7, Hadith 1780 (FR)