Imam Hasan Al-Basri رحمه الله said:

"It will be presented to the son of Adam the moments of his life on the Day of Resurrection.

Every moment he did not do righteous deeds, his soul will break out of sorrow!"

[Hifdhul 'Umr: 63]

Virtues of fasting Ashurah (10 Muharram)

▫️The expiation of sins that is achieved by fasting ‘Ashoora’ refers to minor sins; with regard to major sins, they need separate repentance.

Al-Nawawi (may Allaah have mercy on him) said:

Fasting the day of ‘Arafaah is an expiation for two years, and the day of ‘Ashoora is an expiation for one year, and if a person’s Ameen coincides with the Ameen of the angels, his previous sins will be forgiven… Each of the things mentioned may bring expiation. If he does something that expiates for minor sins he will be expiated, and if there are no minor or major sins, it will be recorded for him as good deeds and he will rise in status thereby… If there is one or more major sins and no minor sins, we hope that it will reduce his major sins.

—Al-Majmoo’ Sharh al-Muhadhdhab, part 6.


Via https://islamqa.info/amp/en/answers/21775

Fasting on Ashura (10th Muharram)
-Reasons for encouraging fasting on Ashura

Via https://islamqa.info/amp/en/answers/21775

When one keeps Quran close to their heart, learn of The Promises and Sunnah of Allah from it, and have full reliance on Him.

Allahumma baarik lahu. Such Iman subhanallah

Do we fast the 9th, 10th, or 11th? | The 4 Levels of Fasting Ashura

| Ash-Shaykh al-Imām Ahmad Musa Jibril (حفظه الله تعالى)

🎥 Everything You Need to Know About the Day of Ashura: https://youtu.be/WPrnCmFPqDY

Training Our Kids to Fast the Day of ‘Āshūrā

| Ash-Shaykh al-Imām Ahmad Musa Jibril (حفظه الله تعالى)

🎥 Everything You Need to Know About the Day of Ashura: https://youtu.be/WPrnCmFPqDY

Once it's Gone, it's Gone 💨

كان محمد بن شهاب الزهري رحمه الله في سفر فصام يوم عاشوراء، فقيل له: تصوم يوم عاشوراء في السفر وأنت تفطر في رمضان؟ فقال: إِنَّ رَمَضَانَ لَهُ عِدَّةٌ مِنْ أَيَّامٍ أُخَرَ، وَإِنَّ عَاشُورَاءَ تَفُوتُ.

Imām al-Zuhrī (d.124H) was traveling on the day of 'Āshūrā while he was fasting. Someone said to him: "You're fasting on the Day of 'Āshūrā while traveling, and yet you break your fast in Ramadān [when traveling]?"

He replied: "[Fasts missed in] Ramadān may be redeemed on other days, but if you miss 'Āshūrā, it can't be so."

• شعب الإيمان للبيهقي (٣٥١٨)

https://www.islamqa.info/amp/en/answers/21787

Praise be to Allah.

Firstly:

You should not observe voluntary fasts when you still owe one or more days from Ramadan, rather you should start with the fasts that you owe from Ramadan, and then observe voluntary fasts.

Secondly:

If you fast the tenth and eleventh of Muharram with the intention of making up days that you owe from Ramadan, that is permissible and will make up for two of the days that you owe. The Prophet (peace and blessings of Allah be upon him) said, “Actions are judged but by intentions, and every person will have but that which he intended.” Fatawa al-Lajnah al-Daa’imah, 11/401

We hope that you will have the reward for making up the missed fast and the reward for fasting that day.

Fatawa Manaar al-Islam, by Shaykh Muhammad ibn ‘Uthaymeen (may Allah have mercy on him), 2/358.

Summary of answer:
If a person intends to do the mustahabb action, that will not be acceptable for the obligatory action. If a person fasts with the intention of 'Ashura, that will not be acceptable as making up for a missed Ramadan fast,

but if he intends to make up the missed Ramadan fast and does that on the day of 'Ashura, then his making up the missed fast will be valid, and there is the hope that he will also attain the reward for 'Ashura, according to some scholars.

https://www.islamqa.info/amp/en/answers/128256