Sahih Bukhari Volume 002, Book 023, Hadith Number 331.
Narated By Al-Bara' bin 'Azib : Allah's Apostle ordered us to do seven things and forbade us to do other seven. He ordered us: to follow the funeral procession. to visit the sick, to accept invitations, to help the oppressed, to fulfill the oaths, to return the greeting and to reply to the sneezer: (saying, "May Allah be merciful on you," provided the sneezer says, "All the praises are for Allah,"). He forbade us to use silver utensils and dishes and to wear golden rings, silk (clothes), Dibaj (pure silk cloth), Qissi and Istabraq (two kinds of silk cloths).