Sahih Muslim Book 1, Hadith Number 184.

Chapter : Beating of the cheeks, tearing of the front opening of the shirt, and calling the calls of the Jihillya (Ignorance) are forbidden.

It is narrated on the authority of Abdullah b. Mas’ud that the Holy Prophet observed: He is not one of us (one among the Ummah of Islam) who beat the cheeks or tore the front opening of the shirt or uttered the slogans of (the days of) Jahiliya (ignorance). Ibn Numair and Abu Bakr said (instead of the word “au”(or) it is “wa” [and] the words are) and tore and uttered (the slogans) of Jahiliya without “alif”.