Answered by Shaykh Jamir Meah
Question: Assalamu alaykum
What is the benefit of fasting for 40 days?
Answer: Wa’alaykum assalam. Jazakum Allah khayr for your question.
I am not aware of the basis for specifically fasting 40 days. It is usually recommended to follow the sunna fasts that have been narrated in the Prophetic Traditions.
The Benefits of 40 days
Though there may not be any authenticated textual basis for fasting for 40 days, 40 days as a period for spiritual and physical discipline, especially breaking unwanted habits, has generally been experienced by spiritual figures, and even many medical professionals, as being a beneficial time frame for long lasting change and personal benefit.
An example of 40 days mentioned in a sound hadith is that the Messenger of Allah ﷺ said, ‘Whoever prays for forty days with the congregation, always being present for the first takbir, it will be written that he will be safe from two things: he will be safe from the Fire and safe from hypocrisy.’ [al Tirmidhi]
Fasting for 40 days
One should be clear why they are doing an act, such as fasting for 40 days, and what they hope to gain from it. The month of Ramadan provides us with the benefits of extended fasting in the year.
For the rest of the year we have the sunna fasts of the Prophet ﷺ who fasted Mondays and Thursdays, and recent research has shown that fasting two days a week has considerable health benefits (see Michael Moseley’s ‘The Fast Diet’), alongside the spiritual benefits and reward we gain from following the sunna of the Prophet ﷺ.
Other sunna fasts once can do are the monthly fasts known as the white days and the black days. The white days are when the moon is at its brightest and these fall on the 13th, 14th, and 15th of each lunar month, while the black days, which are the days when the moon is not visible, are on the 28th, 29th, 30th of each lunar month, or the 1st of the next month if the lunar month is only 29 days. [Bushra al Karim]
Following these weekly and monthly fasts would be a more appropriate and beneficial course of fasting, with the added reward of following the sunna of the beloved Prophet ﷺ.
If for some reason one does choose to fast for long periods of time at a go, then one should only do so if they are physically and mentally able, and there is no fear of consecutive fasting harming them. If they suffer from any serious medical condition, they should consult their medical doctor. Also, they should be sensible in eating and drinking before and after fasting.
[Shaykh] Jamir Meah
Shaykh Jamir Meah grew up in Hampstead, London. In 2007, he traveled to Tarim, Yemen, where he spent nine years studying the Islamic sciences on a one-to-one basis under the foremost scholars of the Ribaat, Tarim, with a main specialization and focus on Shafi’i fiqh. In early 2016, he moved to Amman, Jordan, where he continues advanced studies in a range of Islamic sciences, as well as teaching. Jamir is a qualified homeopath.