Sahih Bukhari Volume 7, Book 72, Hadith Number 740.

Narrated By Al-Bara : The Prophet ordered us to observe seven things: To visit the sick; follow funeral processions; say ‘May Allah bestow His Mercy on you’, to the sneezer if he says, ‘Praise be to Allah!; He forbade us to wear silk, Dibaj, Qassiy and Istibarq (various kinds of silken clothes); or to use red Mayathir (silk-cushions). (See Hadith No. 253 A, Vol. 8).