Abdullah bin Busr narrated from his sister, whose name was Samma’, that the Messenger of Allah (peace be upon him) said: “Do not fast on Saturday except for what has been made obligatory upon you, and if you do not find anything to eat on a Saturday except the bark of a tree, then chew it.”
Hadith Takhrijیہ حدیث صحیح ہے۔ دیکھئے: [أبوداؤد 2436] ، [ترمذي 745] ، [نسائي 2357] ، [ابن ماجه 1739] ، [ابن خزيمه 2165] ، [الطبراني فى معجم الكبير 819، 820، 821] میں مذکور ہے۔
Brief Explanation
(Commentary on Hadith 1786)
That is, he should chew even the bark of a tree, and in one narration it is mentioned that if he finds even a vine of grapes, he should suck it and not fast. There is much discussion regarding the authenticity of this narration. Assuming its authenticity, its meaning would be that he should not fast exclusively on Saturday, but rather, just as with the fast of Friday, he should also fast a day before or a day after. And Allah knows best.