Sunan Abi Dawud, Hadith 2417

Narrated Al-Laith: When it was mentioned to Ibn Shihab (al-Zuhri) that fasting on Saturday had been prohibited, he would say: This is a Himsi tradition.

حَدَّثَنَا عَبْدُ الْمَلِكِ بْنُ شُعَيْبٍ، حَدَّثَنَا ابْنُ وَهْبٍ، قَالَ سَمِعْتُ اللَّيْثَ، يُحَدِّثُ عَنِ ابْنِ شِهَابٍ، أَنَّهُ كَانَ إِذَا ذُكِرَ لَهُ أَنَّهُ نُهِيَ عَنْ صِيَامِ يَوْمِ السَّبْتِ يَقُولُ ابْنُ شِهَابٍ هَذَا حَدِيثٌ حِمْصِيٌّ ‏.‏

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also referenced under: Hadith 2423 (DarusSalam)