Hadith #2421Fasting (Kitab Al-Siyam) · Narrated by Abu Ayyub al-Ansari, Hafs bin 'Umar bin al-Harith حفص بن عمر بن الحارث, Hmam bin Yahya bin Dinar همام بن يحيى بن دينار, Juwayriya bint al-Harith, Muhammad bin Kathir bin Abi 'Ata' محمد بن كثير بن أبي عطاء الثقفي, Qatada قتادة · Sahih
The Prophet (ﷺ) said: Do not fast on Saturday except what has been made obligatory on you; and if one of you can get nothing but a grape skin or a piece of wood from a tree, he should chew it.