From Sahih Bukhari (Hadith 5830):
Narrated Abu `Uthman:While we were with `Utba. `Umar wrote to us: The Prophet (ﷺ) said, "There is none who wears silk in this world except that he will wear nothing of it in the Hereafter." ' Abu `Uthman pointed out with his middle and index fingers. This hadith has also been narrated by Abu `Uthman
Reference: Bukhari 5830