Scholars' opinions on vowing to fast on Friday
11-8-2015 | IslamWeb
Question:
What is the ruling if I vowed to permanently fast every Friday if Allah Almighty healed my mother and she has actually been healed? Does this vow contradict the ruling that fasting on a Friday by itself is disliked? What if the 'Eed occurs on a Friday? In case of inability to fulfill the vow due to sickness or old age, what should I do? How can I get rid of this vow?
Answer:
All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The Hanafi and Maaliki scholars 
have the opinion that fasting on a Friday alone is permissible and that the vow to fast on this day is binding. They argue that it is a vow to obey Allaah Almighty, quoting the Hadeeth in which the Prophet, sallallaahu ‘alayhi wa sallam, says: "Whoever vowed to obey Allaah should obey Him." [Al-Bukhari]
The Shaafi‘i and Hanbali scholars hold the opinion that it is disliked in the Sharee'ah to fast a Friday by itself. This is the preponderant opinion based on the following Ahaadeeth:
• It was narrated on the authority of Muhammad ibn ‘Abbad ibn Ja‘far 
that he said:
I asked Jabir ibn ‘Abdullaah 
as he was circumambulating the Ka'ba, whether the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, forbade fasting on Friday, whereupon he said: "Yes, by the Lord of this House." [Muslim]
• It was narrated on the authority of Abu Hurayrah 
that he said: "I heard the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, say, 'None of you should fast on a Friday unless he fasts a day before or after it.'" [Al-Bukhari]
• It was also narrated on the authority of Abu Hurayrah that the Prophet, sallallaahu ‘alayhi wa sallam, said: "Do not single out the night of Friday with prayer or good deeds from among the other nights, and do not favor Friday with fasting apart from other days unless it coincides with a day that you are accustomed to fast." [Muslim]
In his commentary on Saheeh Muslim, An-Nawawi said:
These Ahaadeeth evidently support the opinion of the majority of the Shaafi‘i scholars and those who agree with them. They all view that it is disliked to fast on a Friday by itself unless it coincides with a day that one is accustomed to fast. If one fasts a day before or after Friday or it coincides with a day that he is accustomed to fast, as when one vows to fast the day when a dear patient is healed and that then happens on a Friday, then fasting on a Friday is not disliked in such cases, based on the mentioned Ahaadeeth. As for Maalik's statement in Al-Muwatta’, "I never heard any of the scholars of Fiqh or those whose opinion is followed forbid fasting on a Friday. Rather, fasting on this day is a good deed. Even, I know some scholars who fasted on this day and were keen to fast it in particular;" this was his personal opinion. Other scholars adopted a contradictory opinion. However, the Ahaadeeth of the Prophet, sallallaahu ‘alayhi wa sallam, take precedence over personal opinions. It is proven that fasting on a Friday by itself is disliked; so that is the opinion that should be adopted. Maalik is excused because the Hadeeth did not reach him. Ad-Dawoodi, a student of Maalik, said, "This Hadeeth did not reach Maalik. Had it (the Hadeeth) reached him, then he (Maalik) would not have contradicted it."
As for the fulfillment of a vow to fast on Friday, there is a difference in opinions among the Shaafi‘i and the Hanbali scholars . The Shaafi‘i scholars hold the opinion that fulfillment is binding whether one vows to fast the Friday alone or with other days. They mentioned two reasons to justify why they believe that fasting is binding although it is disliked and they at the same time believe that disliked fasting is not binding:
First: Fasting on a Friday is not disliked because of the day, but because of the idea of singling out the day with fasting. Therefore, when one specifies in his vow that he fasts the Friday only, as when he says "I vow to fast on Friday alone," then the vow is not binding. This is unlike the case when the vow is not specified. In the latter case, the vow is binding because one can avoid what is disliked by fasting another day before or after it.
Second: Fasting on a Friday by itself is disliked when it is voluntary, not obligatory, fasting.
The Hanbali scholars hold the opinion that it is recommended for a person who vowed to fast on Friday by itself not to do so and to offer an expiation like that for breaking an oath instead. That is because abandoning doing what is disliked is better than doing it. On the other hand, fasting absolves one of the liability and then he does not need to offer the due expiation.
The preponderant opinion is that of the majority of scholars; that it is binding to fulfill this vow, unless one is unable to do so. In the latter case, one may offer an expiation as for an oath. It was narrated on the authority of ‘Uqbah ibn ‘Amir that the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, said: "The expiation of a vow is the same as the expiation of (breaking) an oath." [Muslim]
When a Friday coincides with a day when it is prohibited to fast on, such as the two days of 'Eed, then it is obligatory that one breaks his fast and then makes up for the missed day later. In Al-Umm, Ash-Shaafi‘i said: "Whoever vowed to fast on Friday and it coincided with a day that must not be fasted is required to break the fast and then make it up later."
If one is unable to fulfill the vow, then he is required to offer the expiation of an oath, as stated earlier. If one is able to fulfill the vow, then there is no way for him to be absolve of his liability except by fulfilling it.
Allaah Knows best.