Musnad Ahmad 243
It was narrated that Abu `Uthman said:
We were with `Utbah bin Farqad and `Umar رضي الله عنه wrote to him about things he narrated from the Prophet (ﷺ). Among the things he wrote was that the Messenger of Allah (ﷺ) said: `No one wears silk in this world except one who will not wear it in the Hereafter, except this much,` and he gestured with his two fingers, the forefinger and the middle finger. Abu `Uthman said: I thought this referred to the edging of the tayalisah (a shawl-like garment) when we first saw the tayalisah.
حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، حَدَّثَنَا التَّيْمِيُّ، عَنْ أَبِي عُثْمَانَ، رَضِيَ اللَّهُ عَنْهُ قَالَ كُنَّا مَعَ عُتْبَةَ بْنِ فَرْقَدٍ فَكَتَبَ إِلَيْهِ عُمَرُ رَضِيَ اللَّهُ عَنْهُ بِأَشْيَاءَ يُحَدِّثُهُ عَنْ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَكَانَ فِيمَا كَتَبَ إِلَيْهِ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ لَا يَلْبَسُ الْحَرِيرَ فِي الدُّنْيَا إِلَّا مَنْ لَيْسَ لَهُ فِي الْآخِرَةِ مِنْهُ شَيْءٌ إِلَّا هَكَذَا وَقَالَ بِإِصْبَعَيْهِ السَّبَّابَةِ وَالْوُسْطَى قَالَ أَبُو عُثْمَانَ فَرَأَيْتُ أَنَّهَا أَزْرَارُ الطَّيَالِسَةِ حِينَ رَأَيْنَا الطَّيَالِسَةَ‏.‏