Riyad as-Salihin, Book 18, Hadith 1658 (In-Book)

Ibn Mas'ud (May Allah be pleased with him) said: The Messenger of Allah said, "He who (on befalling a calamity) slaps his cheeks, tears his clothes and follows the ways and traditions of the Days of Ignorance is none of us."[Al-Bukhari and Muslim].

وعن ابن مسعود رضي الله عنه قال‏:‏ قال رسول الله صلى الله عليه وسلم ‏:‏‏ "‏ليس منا من ضرب الخدود، وشق الجيوب، ودعا بدعوى الجاهليه‏" ‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏

sunnah.com