Sahih al-Bukhari 5828
Narrated Aba `Uthman An-Nahdi:
While we were with `Utba bin Farqad at Adharbijan, there came `Umar's letter indicating that Allah's 
Apostle had forbidden the use of silk except this much, then he pointed with his index and middle 
fingers. To our knowledge, by that he meant embroidery.
حَدَّثَنَا آدَمُ، حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا قَتَادَةُ، قَالَ سَمِعْتُ أَبَا عُثْمَانَ النَّهْدِيَّ، أَتَانَا كِتَابُ عُمَرَ وَنَحْنُ مَعَ عُتْبَةَ بْنِ فَرْقَدٍ بِأَذْرَبِيجَانَ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم نَهَى عَنِ الْحَرِيرِ، إِلاَّ هَكَذَا، وَأَشَارَ بِإِصْبَعَيْهِ اللَّتَيْنِ تَلِيَانِ الإِبْهَامَ قَالَ فِيمَا عَلِمْنَا أَنَّهُ يَعْنِي الأَعْلاَمَ‏.‏