In the Name of Allāh, the Most Merciful, the Giver of Special Mercy

All praise is due to Allāh the Most High and Most Great, the One Who is alone in creating and controlling, the One Who honoured His friends with His help, and humiliated His enemies through His forsaking [of them], so how excellent a Protector is our Lord, and how excellent a Helper is He.

I testify that there is none worthy of worship except Allāh alone without any partners, to Him belong the Kingdom and praise, and He is, over all thing, completely capable. And I bear witness that Muḥammad is His slave and His Messenger; the bringer of glad tidings, the warner, and shining lantern, may the praise and protection of Allāh be upon him, his family, his Companions, and those who follow them in excellence until the Day of Recompense.

To proceed:

Indeed, in this month, the month of Muḥarram, was the salvation of Mūsá, may praise and protection be upon him, and his people from the enemy of Allāh – Pharaoh and his army. By Allāh it was a major blessing obligating gratitude towards Allāh the Almighty and Majestic. This is why, when the Prophet ﷺ arrived in al-Madīnah, and he found the Jews fasting the tenth day of this month, the Prophet ﷺ said, “I have more right to Mūsá than you”, thus he fasted it and commanded its fasting. He was asked about the virtue of fasting it and he said, “I hope in Allāh that it may expiate for (the sins of) the year that came before it.” After that he commanded contradicting the Jews by fasting the tenth and a day before it which is the ninth, or a day after it which is the eleventh.

Consequently, it is best to fast the tenth day and add to it a day before it, or a day after it. Adding the ninth day to it is better than the eleventh.

Thus, it is necessary for you, my Muslim brother, to fast the Day of ʿĀshūrāʾ, likewise the ninth day, in order to actualise contradicting the Jews which the Messenger of Allāh ﷺ commanded.

May Allāh facilitate success for me and you to be grateful for His blessings, and worship Him with excellence, and may He protect us from the evils of our souls through His care – indeed He is the Most Generous and Most Bountiful.

I have no objections to spreading it (i.e., this letter).

Written by Muḥammad al-Ṣāliḥ al-ʿUthaymīn 21/12/1409.

Source: Majmūʿ al-Fatāwá (20: 39-40).