Sahih Bukhari Volume 8, Book 73, Hadith Number 241.

Narated By Al-Bara : The Prophet ordered us to do seven (things) and forbade us from seven (other things): He ordered us to pay a visit to the sick, to follow funeral possessions, to say: May Allah be merciful to you to a sneezer, – if he says: Praise be to Allah, to accept invitation (invitation to a wedding banquet), to return greetings, to help the oppressed, and to help others to fulfill their oaths (provided it was not sinful). And he forbade us from seven (things): to wear golden rings or golden bangles, to wear silk (cloth), Dibaj, Sundus and Mayathir.