Is fasting on Mondays and Thursdays a sunnah?

Why the scholars hold this

The ruling rests on a narration in which the Prophet ﷺ was asked about these two days and gave the reason for singling them out. The wording is reported by Usamah ibn Zayd رضي الله عنه:

"Those are two days on which deeds are presented to the Lord of the worlds, and I love that my deeds be presented while I am fasting."— Sunan al-Nasa'i 2358, from Usamah ibn Zayd

Shaykh Ibn Baz رحمه الله draws the conclusion directly from this: the Prophet ﷺ did it, was asked why, and answered — so it is a sunnah for the believing man and woman whenever it is easy for them. Ibn 'Uthaymeen رحمه الله, in al-Sharh al-Mumti', notes that Monday is the more emphasised of the two, and that the Prophet ﷺ gave a second reason for Monday specifically: it is the day he was born and the day on which revelation came to him.

It is recommended, never required

The scholars are consistent on this point, and it is the practical heart of the answer.

• Not an obligation: Shaykh Ibn Baz رحمه الله says it is mustahabb (recommended), not wajib. Whoever fasts is rewarded; whoever does not is not sinning.
• No sin in stopping: asked about someone who cannot fast them consistently because of illness or inability, he answered that there is no blame — whether one fasts some days or some months and leaves others.
• One day is enough: you do not have to fast both. Ibn Baz رحمه الله states clearly that joining the two is not required; fasting either one alone carries its reward. IslamWeb (fatwa 101641) agrees that fasting them together is better, but that whoever fasts Thursday alone or Monday alone still has the reward of that fast.
• Any month counts: the virtue is not tied to a particular month. Ibn Baz رحمه الله was asked about Rajab and Sha'ban and answered that there is no harm in fasting them in any month. IslamWeb (fatwa 98354) adds that in Rajab the recommendation has two supports: the general merit of fasting in the sacred months, and the standing recommendation of these two days in every month.

The one condition that changes things

For a married woman, the voluntary fast is tied to her husband's permission. Shaykh Ibn Baz رحمه الله explains that she should not fast a voluntary fast without his permission when he is present, because the Prophet ﷺ prohibited it:

"It is not for a woman to fast while her husband is present except with his permission."— Sahih al-Bukhari 5192

This applies to Mondays and Thursdays, to the six days of Shawwal, and to the three days of each month alike. Ramadan is excluded — it is obligatory on everyone. If the husband is absent, travelling, then there is no harm in her fasting without his permission.

If you have made a vow

The voluntary nature of the fast changes if you have taken a vow (nadhr) to fast these days. Ibn Baz رحمه الله makes the exception explicit: if a person vows to fast Mondays and Thursdays, the fast becomes binding and must be fulfilled, because the Prophet ﷺ said:

"Whoever vows to obey Allah, let him obey Him."— Sahih al-Bukhari 6696

Short of a vow, the matter remains entirely open — fast when you are able, and there is no blame when you are not.

In practice

If you want to take this up, the simplest form is to fast Monday and Thursday each week, or whichever of the two fits your circumstances. If one day is difficult, fast the other. If a week passes and you cannot, you have lost a recommended act, not committed a sin. And if you are a married woman, settle the matter with your husband first when he is at home.

Key takeaways

• Fasting Mondays and Thursdays is a confirmed sunnah, established by the Prophet's ﷺ own practice and his stated reason: deeds are presented to Allah on those days.
• It is recommended, not obligatory — leaving it off is not a sin, and no blame attaches to fasting irregularly or for a valid excuse.
• You may fast either day alone; joining them is better but not required.
• A married woman needs her husband's permission for these voluntary fasts when he is present; Ramadan is exempt.
• If you have vowed to fast them, the fast becomes binding and must be fulfilled.

Further reading

• al-Sharh al-Mumti' 'ala Zad al-Mustaqni', Ibn 'Uthaymeen — the chapter on voluntary fasting
• Majmu' Fatawa wa Maqalat, Shaykh Ibn Baz

And Allah knows best.