Bukhari :: Book 7 :: Volume 72 :: Hadith 719
Narrated Abu 'Uthman:
While we were at Adharbijan, 'Umar wrote to us: 'Allah's Apostle forbade wearing silk except this much. Then the Prophet approximated his two fingers (index and middle fingers) (to illustrate that) to us.' Zuhair (the sub-narrator) raised up his middle and index fingers.
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