Dear scholar, as-salamu `alaykum. I want to know the Islamic position on fasting voluntarily on a Saturday.
If it happens that the Day of Arafah—or any other recommended day for fasting—falls on a Friday or Saturday, it will be permissible to fast on it.
As for optional fasting, Muslims are highly recommended by the Sunnah to fast certain days, such as fasting of the day of Arafah, the White Days (13th, 14th, and 15th of every lunar month), the day of Ashura (10th of Muharram), and the six days of Shawwal.
If it happens that one of these days is Friday or Saturday, there is no problem in fasting it. A Muslim would fast on such a day because it is Arafah or Ashura not because it is Saturday or Friday.
Prophet Muhammad (peace and blessings of Allah be upon him) came to Juwayriyyah bint Al-Harith (one of the Prophet’s wives) one Friday and found her fasting. He asked her, “Did you fast yesterday?” She said, “No.” He asked, “Do you intend to fast tomorrow?” She said, “No.” He said, “Then, break your fast.” (Al-Bukhari)
Prophet Muhammad also (peace and blessings of Allah be upon him) said, “Don’t single out Friday with fasting except when you fast a day before or after it.” (Al-Bukhari and Muslim)
Given the above, what is disliked—according to some scholars—for a Muslim is to single out Friday or Saturday with fasting.
So, if one fasts a day before or after a Friday/Saturday, it will be OK.
If it happens that Arafah—or any other recommended day for fasting—falls on a Friday or Saturday, it will be permissible to fast on it.
Allah Almighty knows best.
