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." (ES)
English reference (ES): Vol. 1, Book 7, Hadith 1709 (ES)
Arabic reference (ES): Book 7, Hadith 1780 (ES)