Sahih Muslim — The Book of Clothes and Adornment — Hadith No: 5411
Translation
Asim al-Abwal reported on the authority Abu Uthman saying:'Umar wrote to us when we were in Adharba'ijan saying: 'Utba b. Farqad, this wealth is neither the result of your own labour nor the result of the labour of your father, nor the result of the labour of your mother, so feed Muslims at their own places as you feed (members of your family and yourselves at your own residence), and beware of the life of pleasure, and the dress of the polytheists and wearing of silk garments, for Allah's Messenger (ﷺ) forbade the wearing of silk garments, but only this much, and Allah's Messenger (ﷺ) raised his. forefinger and middle finger and he joined. them (to indicate that only this much silk can be allowed in the dress of a man). 'Asim said also: This is what is recorded in the lette., (sent to us), and Zuhair raised his two fingers (to give an idea of the extent to which silk may be used)