Riyad Us-Saliheen (Gardens of the Righteous)
Chapter 345
Abomination of Selecting Friday for Fasting
1760. Abu Hurairah (May Allah be pleased with him) reported: The Prophet (PBUH) said, "Do not choose the Friday night among all other nights for standing in (Tahajjud) prayer, and do not choose Friday among all other days for Saum (fasting) except that one you have accustomed to.''
[Muslim].
Commentary: It is undesirable to fix Jumu`ah for voluntary fast. One can, however, observe fasting if Friday occurs in his routine of fasts, i.e., if one observes fast on alternate days and Jumu`ah occurs on the day when he observes fast, or if one observes the fast of the Day of `Arafah, or the Day of `Ashura', and Friday occurs on that day, or if Friday occurs during the Ayyam Al-Beid, or Friday occurs when one is observing fasts of Nadhr (fasts one has vowed for). There is no harm in observing fast on Friday in all such cases but its special observance on Friday is not recommended.
1761. Abu Hurairah (May Allah be pleased with him) said: I heard the Messenger of Allah (PBUH) as saying: "None of you should observe fast on Friday except that he should observe fast either one day before it or one day after it.''
[Al-Bukhari and Muslim].
Commentary: We learn from this Hadith that we can fast on Friday if we fast, along with it, on Thursday or Saturday, i.e., either one day before or after it.
1762. Muhammad bin `Abbad (May Allah be pleased with him) said: I asked Jabir (May Allah be pleased with him). Did the Prophet (PBUH) prohibit fasting on Friday?'' He said, "Yes.''
[Al-Bukhari and Muslim].
1763. Juwairiyah bint Al-Harith (May Allah be pleased with her), the Mother of the Believers, said that the Prophet (PBUH) visited her on a Friday and she was observing fast. He asked, "Did you observe fast yesterday?'' She said, "No.'' He asked, "Do you intend to observe fast tomorrow?'' She said, "No.'' He said, "In that case, give up your fast today.''
[Al-Bukhari].
Commentary: We learn from this Hadith that if someone is keeping fast on Friday and has not fasted the day before, nor does he intend to fast the following day, i.e., Saturday, it is permissible for him to break his fast.