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.

حَدَّثَنَا أَحْمَدُ بْنُ يُونُسَ، حَدَّثَنَا زُهَيْرٌ، حَدَّثَنَا عَاصِمٌ، عَنْ أَبِي عُثْمَانَ، قَالَ كَتَبَ إِلَيْنَا عُمَرُ وَنَحْنُ بِأَذْرَبِيجَانَ أَنَّ النَّبِيَّ ﷺ نَهَى عَنْ لُبْسِ الْحَرِيرِ إِلاَّ هَكَذَا، وَصَفَّ لَنَا النَّبِيُّ ﷺ إِصْبَعَيْهِ. وَرَفَعَ زُهَيْرٌ الْوُسْطَى وَالسَّبَّابَةَ.