Imam Ibn Baaz was asked about singling out fasting Friday to make up for a Missed fast and not fasting it voluntarily. Is it obligatory to fast a day before it or a day after it as well?
As for the Voluntary fast, then it’s a must to fast a day before it or a day after it, because the messenger صلى الله عليه و سلم prohibited that Friday be fasted. He said:
“except that you fast a day before it or a day after it”
And when one of his صلى الله عليه و سلم wives fasted Friday, he said, “did you fast yesterday?” She said, “No”. He said, “Will you fast tomorrow?” She said, “No” He said, “(thus) break your fast.”
As for if it is to make up a missed obligatory fast, then there is no problem If Allah Wills because he didn’t specify Friday (to make it up).
Rather, Friday coincided with his time of rest and not working or for other reasons. Thus he fasted Friday to make up that which he missed from Ramadan or to make up (a fast for) an oath, or other than that.
Thus, he didn’t specify it due to its virtue. Rather, he fasted it because it is easier for him to make up that which he missed due to work.
If he fasted along with it a day before it or a day after it by way of precaution, then it is better than making it up (by fasting Friday alone. Thus he fasts two days together or three days – Thursday, Friday, and Saturday – so that he can be distanced from doubtful matters.
“Leave that which makes you doubt for that which doesn’t make you doubt”
As for the prohibition, then it has come in regards to voluntary fasting in it (Friday), one doesn’t voluntarily fast in it by singling it out. Rather he fasts (with it) a day before it or a day after it.
Majid Jawed Al-Afghanee