Fasting on the 9th and 10th of Muharram is recommended because the 10th day, called Ashura, is a special day in Islam tied to gratitude, remembrance, and the Sunnah of Prophet Muhammad. The 9th is often added so the fast is distinguished from other communities and to follow the Prophet’s reported intention to fast both days.

Why these days matter

  • 10th Muharram (Ashura): Muslims fast this day to follow the Prophet’s practice and to remember the day Allah saved Prophet Musa and his people from Pharaoh.
  • 9th Muharram (Tasu’a): The Prophet is reported to have intended to fast the 9th as well, so many scholars recommend fasting 9th and 10th together.
  • Spiritual reward: Fasting Ashura is described in the sources as an expiation for the sins of the previous year, for minor sins.

Main reasons

  1. It follows the Sunnah of the Prophet.
  1. It expresses gratitude to Allah for saving Musa and the believers.
  1. It distinguishes the Islamic fast from other traditions by adding an extra day.

How Muslims fast it

Common practice is:

  • Fast the 9th and 10th of Muharram.
  • Or fast the 10th and 11th if someone misses the 9th.
  • At minimum, many scholars say fasting the 10th alone is valid, though fasting two days is better.

Note

This fast is voluntary , not obligatory, unlike Ramadan.

TL;DR: Muslims fast 9th and 10th Muharram to follow the Prophet’s Sunnah, thank Allah for the salvation of Musa, and seek forgiveness for the previous year’s minor sins.