«كان عاشوراء يوما يصومه أهل الجاهلية فمن أحب منكم أن يصومه فليصمه ومن كرهه فليدعه»
The Prophet (peace and blessings be upon him) said:
"Ashura was a day on which the people of the Jahiliyyah used to fast. So whoever among you wishes to fast it, let him fast it, and whoever wishes to leave it, let him leave it."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4457