'A'isha (Allah be pleased with her) reported that the Messenger of Allah (ﷺ) had ordered to observe fast (on 'Ashura) before the fasting in Ramadan was made obligatory. But when it became obligatory, then he who wished fasted on the day of Ashura, and he who wished did not observe it (on that day).
Reference | : Sahih Muslim 1125d |
In-book reference | : Book 13, Hadith 146 |
USC-MSA web (English) reference | : Book 6, Hadith 2502 |
(deprecated numbering scheme) |