Sahih Muslim | Book 24 | Hadith Number 5156

Narrated by Suwaid b. Ghafala
Suwaid b. Ghafala said: 'Umar addressed us at a place known as Jabiya (Syria) and he said: Allah's Apostle (may peace be upon him) forbade us the wearing of silk but to the extent of two or three fingers or four fingers.