Imams Abu Dawud and Tirmidhi (rahimahumallah) have reported from Sayyidatuna Samma (radiyallahu’anha) that Rasulullah (sallallahu’alaihi wasallam) said: “Don’t fast on Saturdays unless it’s an obligatory fast” i.e, like Ramadan.
(Sunan Abi Dawud, Hadith: 2413, Sunan Tirmidhi, hadith: 744 and others)
This Hadith has been quoted by some contemporaries to discourage people from fasting on the 10th of Muharram, or even the 9th or 11th of Muharram, if any of these dates fall on a Saturday.
This is a gross misinterpretation which stems from a lack of faqahah (true understanding of the nature of Shari’ah)
Hereunder is a brief explanation of the issue as understood by the senior Scholars of the ummah.
The Scholars have either interpreted the above Hadith differently, classified it to be abrogated or even dismissed it as weak. The details are as follows:
1. Imams Bukhari and Muslim have reported via Sayyiduna Abu Hurairah (radiyallahu’anhu) that Rasulullah (sallallahu’alaihi wasallam) said: “None of you should fast on a Friday, unless he fasts with it one day before or after.” (Sahih Bukhari, hadith:1985 and Sahih Muslim, 2678)
This Hadith clearly states that there is no harm if one observes a fast on a Friday and Saturday together. Hence the Hadith that prohibits fasting on Saturdays will be interpreted to mean: fasting on a Saturday only.
Note: Those who have the habit of dismissing everything that doesn’t suite them as a “weak Hadith”, should take note that this Hadith is in Sahih Bukhari and Sahih Muslim. The next Hadith is also classified sahih:
2. Sayyidatuna Ummu Salamah (radiyallahu ‘anha) – the honourable wife of Rasulullah (sallallahu’alaihi wasallam)- reports that: “Rasulullah (sallallalhu ’alayhi wasallam) would fast on Saturdays and Sundays more than any other days”
(Musnad Ahmad, vol.6 pg.324 and classified sahih (authentic) by Imams Ibn Khuzaymah & Ibn Hibban; see Sahih Ibn Khuzaymah, hadith: 2167 & Sahih Ibn Hibban, hadith:3616)
Interestingly both Imams; Ibn Khuzaymah and Ibn Hibban (rahimahumallah) have recorded this Hadith in the ‘Chapter which explains the permissibility of fasting on a Saturday coupled with another day.’
3. Hafiz Ibn Rajab Al-Hambali (rahimahullah) says: “In light of this, we will interpret the narration that prohibits fasting on Saturdays to mean fasting on a Saturday alone.” (Lataiful Ma’arif, pg.112)
4. In fact, Imam Bayhaqi (rahimahullah) quoted the Hadith of prohibition in a chapter named: ‘Chapter that discusses the narrations that prohibit fasting on a Saturday alone’
In other words, Imam Bayhaqi has also concurred with the conclusion that the Hadith doesn’t stop one from fasting on a Saturday as long as one fasts a day before or after as well. For this reason Bayhaqi (rahimahullah) ends the chapter with the Hadith of Umm Salamah (radiyallahu’anha) –cited above- that Rasulullah (sallallahu’alayhi wasallam) would often fast on Saturdays and Sundays. (Sunanul Kubra, vol.4 pg.302-303)
Note: There are many Scholars who have adopted the above interpretation. I have not quoted them to avoid monotony. In fact, even Imam Tirmidhi (rahimahullah) -after recording this Hadith- states: ‘The meaning of this prohibition is when a man singles out the day of Saturday for fasting, since the Jews revere this day only. (Sunan Tirmidhi, hadith: 744)
5. Imam Tahawi (rahimahullah) writes: “It’s possible that the prohibition applies to those who do so solely to replicate the Jews. If someone fasts on Saturday without the intention of emulating of the Jews, then it will not be makruh (disliked)” (Sharh Ma’anil Aathaar, vol.2 pg.81)
Those who claimed abrogation
6. Imam Abu Dawud (rahimahullah) after citing this narration in his sunan writes:
“This narration is abrogated by the Hadith reported by Sayyidatuna Juwairiyah (radiyallahu ‘anha) wherein she reports that Rasulullah (sallallahu ‘alayhi wasallam) visited her on a Friday and discovered she was fasting. He enquired: “did you fast yesterday?” She replied: “no” he asked further: “do you intend to fast tomorrow (Saturday)? She said: “no”
Rasulullah (sallallahu’alayhi wasallam) said: “Then don’t fast today”
(Sahih Bukhari, 1986, Sunan Abi Dawud, 2414)
By quoting this Imam Abu Dawud (rahimahullah) is emphasising that the Nabi of Allah (sallallahu ‘alayhi wasallam) saw nothing wrong with fasting on a Saturday.
7. Like Imam Abu Dawud has done, Imam Bayhaqi (rahimahullah) also quoted the Hadith of Sayyidatuna Juwairiyyah (rahiyallahu’anha) in answer to the Hadith of prohibition. (Sunanul Kubra, vol.4 pg.303)
8. Ibn Taymiyyah (rahimahullah) says: This Hadith is either shazh (unacceptable due to contradiction) or Mansukh; abrogated”
Those who deemed it as a weak narration
9. Imam Abu Dawud (rahimahullah) quotes Imam Malik (rahimahullah) to have said: “This is a mistake” Sunan Abi Dawud, 2416)
10. He also quotes that whenever the narration that prohibits fasting on Saturdays was mentioned before Imam Zuhri (rahimahullah) he would say that it’s unreliable. (Sunan Abi Dawud, 2415. See Shaykh Muhammad ‘Awwamah’s footnotes explaining Zuhri’s statement.)
Imam Tahawi (rahimahullah) has also said that Imam Zuhri discredited this Hadith. (Sharh Ma’anil Aathar, vol.2 pg.81)
11. Imam Nasaai (rahimahullah) after reporting this Hadith comments: “This Hadith is very contradictory” (Talkheesul Habeer, vol.2 pg.470)
12. Imam Tahawi (rahimahullah) says: “The Hadiths that permit fasting on a Saturday are more popular and acceptable to the ‘Ulama in comparison to this (Hadith of prohibition) which is shazh (unacceptable due to contradiction) (Sharhul Ma’ani, vol2 pg.80)
13. Ibn Taymiyyah (rahimahullah) says: This Hadith is either shazh (unacceptable due to contradiction) or Mansukh; abrogated”
14. Hafidh Ibn Hajar (rahimahullah) says: “Such contradiction in a narration like this one is sufficient to weaken it.” (Talkheesul Habeer, vol.2 pg.470)
Note: It’s truly amazing how some people (when it suites them) choose to follow a Hadith as debatable as this one and ignore other Hadiths that are authentic (like the Hadith of Bukhari/Muslim and the other from Sahih Ibn Hibban)
15. Imam Tahawi (rahimahullah) writes in his unique Hadith collection entitled: Sharh ma’ani Aathaar” “Indeed Rasulullah (sallallahu’alaihi wasallam) permitted and encouraged fasting on ‘Aashura, and he never said: “Don’t fast (‘Aashura) if it falls on a Saturday”, Tahawi writes further:
“That’s a proof to show that the (‘Aashura) fast can be observed on any day” (Vol.2 pg.80)
In light of the above, one will be allowed to fast on ‘Aashura if it falls on a Saturday as long as it’s not done in emulation of the Jews and/or one adds a day before or after it. This is supported by authentic Hadiths.
As for the Hadith that apparently prohibits fasting on a Saturday other than for the obligatory fast; together with it being classified as either abrogated or weak by the Senior Scholars of the Ummah, it also has a different interpretation.
In fact, some of the earlier scholars actually refused to quote this narration to anyone, for fear of creating confusion (like is the sad case today)
 See an interesting discussion on the details of this abrogation by Hafiz Ibn Hajar (rahimahullah) in Talkheesul Habeer, vol.2 pg.480.