The hadith prohibiting fasting on Saturday is not authentic
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Question: Is the hadith prohibiting fasting on Saturday except for what is obligatory upon us authentic?
Answer: The hadith mentioned is not authentic due to its inconsistency, as many of the memorizers have pointed out. This is because it is authentic from the Prophet (peace and blessings be upon him) that he said:Bulugh al-Maram 5:41 It is agreed upon that it is authentic. The day following it is Saturday.
The hadith mentioned is explicit in the permissibility of fasting it as a voluntary act along with Friday. It is also authentic from him (peace and blessings be upon him) that he used to fast on Saturday and Sunday, and he would say:Bulugh al-Maram 5:44 Al-Nasa'i narrated it, and Ibn Khuzaymah graded it as authentic.
Answer: The hadith mentioned is not authentic due to its inconsistency, as many of the memorizers have pointed out. This is because it is authentic from the Prophet (peace and blessings be upon him) that he said:
None of you should fast on Friday, unless he fasts together with the day before or the day after.
لا تصوموا يوم الجمعة إلا أن تصوموا يومًا قبله أو يومًا بعدهThe hadith mentioned is explicit in the permissibility of fasting it as a voluntary act along with Friday. It is also authentic from him (peace and blessings be upon him) that he used to fast on Saturday and Sunday, and he would say:
They are the 'ids of the polytheists, and I love to act contrary to what they do.
إنهما يوما عيد للمشركين وأنا أريد أن أخالفهم
Source
binbaz.org.sa
The Arabic text is copied verbatim from the original source, without any edits.