Sahih Ibn Khuzaymah 2165 — the ahadith of the Noble Prophet

Imam Abu Bakr, may Allah have mercy on him, says that the ahadith of the Noble Prophet (peace and blessings be upon him) in which he forbade fasting on Friday alone, except if one fasts a day before Friday or a day after it, contain evidence that the Prophet (peace and blessings be upon him) permitted fasting on Saturday, provided that one fasts on Friday before it or on the day after it (Sunday).