Sahih Al Bukhari Hadith Number 1298

Narrated `Abdullah: The Prophet (peace be upon him) said, “He who slaps the cheeks, tears the clothes and follows the traditions of the Days of Ignorance is not from us.”

23  Funerals (Al-Janaa’iz)
Hadith number 1298
Volume no 2
Chapter: 39 (Prohibition of wailing and following the traditions of the Days of Ignorance when afflicted with a calamity)