Sahih Muslim Book - 37, Hadith - 5411

حَدَّثَنَا أَحْمَدُ بْنُ عَبْدِ اللهِ بْنِ يُونُسَ ، حَدَّثَنَا زُهَيْرٌ ، حَدَّثَنَا عَاصِمٌ الأَحْوَلُ ، عَنْ أَبِي عُثْمَانَ ، قَالَ: كَتَبَ إِلَيْنَا عُمَرُ وَنَحْنُ بِأَذْرَبِيجَانَ: يَا عُتْبَةُ بْنَ فَرْقَدٍ ، إِنَّهُ لَيْسَ مِنْ كَدِّكَ ، وَلاَ مِنْ كَدِّ أَبِيكَ ، وَلاَ مِنْ كَدِّ أُمِّكَ ، فَأَشْبِعِ الْمُسْلِمِينَ فِي رِحَالِهِمْ مِمَّا تَشْبَعُ مِنْهُ فِي رَحْلِكَ ، وَإِيَّاكُمْ وَالتَّنَعُّمَ ، وَزِيَّ أَهْلِ الشِّرْكِ ، وَلَبُوسَ الْحَرِيرَ ، فَإِنَّ رَسُولَ اللهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ نَهَى عَنْ لَبُوسِ الْحَرِيرِ ، قَالَ: إِلاَّ هَكَذَا ، وَرَفَعَ لَنَا رَسُولُ اللهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِصْبَعَيْهِ الْوُسْطَى وَالسَّبَّابَةَ وَضَمَّهُمَا. قَالَ زُهَيْرٌ: قَالَ عَاصِمٌ : هَذَا فِي الْكِتَابِ ، قَالَ: وَرَفَعَ زُهَيْرٌ إِصْبَعَيْهِ.

It was narrated that Abu 'Uthman said: "Umar wrote to us when we were in Azerbaijan, (saying): 'O 'Utbah bin Farqad, it is not by your efforts or by the efforts of your father or the efforts of your mother. Feed the Muslims in their places from that which you feed yourself in your place. Beware of luxury and the garments of the people of Shirk and garments of silk, for the Messenger of Allah (s.a.w) forbade garments of silk and said except this much, and the Messenger of Allah (s.a.w) held up his forefinger and middle finger, holding them together.'" Zuhair said: "Asim said: 'It is in the book,"' and Zuhair held up his two fingers.