Umar wrote to us while we were in Azerbaijan, "Utba bin Farqad, this wealth is not from your toil, nor from the toil of your father, nor from the toil of your mother. So feed the Muslims in their camps from what fills you in your own camp. Beware of luxury, the dress of the polytheists, and the wearing of silk, for the Messenger of Allah ﷺ forbade the wearing of silk."He said, "Except like this," and the Messenger of Allah ﷺ raised two of his fingers for us, the middle finger and the index finger, holding them together.Zuhayr said, Asim said, "This is in the letter." He said, and Zuhayr raised his two fingers.
كتب إلينا عمر، ونحن بأذربيجان: يا عتبة بن فرقد، إنه ليس من كدك، ولا من كدك، ولا من كد أبيك، ولا من كد أمك، فأشبع المسلمين في رحالهم مما تشبع منه في رحلك، وإياكم والتنعم، وزي أهل الشرك، ولبوس الحرير، فإن رسول الله ﷺ نهى عن لبوس الحرير، قال: إلا هكذا، ورفع لنا رسول الله ﷺ إصبعيه: الوسطى والسبابة وضمهما. قال زهير: قال عاصم: هذا في الكتاب، قال: ورفع زهير إصبعيه.
Bukhari reported it in the Book of Clothing (5829), and Muslim in the Book of Clothing (2069:12), both from Ahmad bin Abdullah bin Yunus, who said, Zuhayr narrated to us, who said, Asim Ahwal narrated to us, from Abu Uthman, and he mentioned it. The wording is Muslim's.