The Messenger of Allah ﷺ said, "There are two practices among people that constitute disbelief, attacking someone's lineage and wailing over the dead."
قال رسول الله ﷺ: اثنتان في الناس هما بهم كفر: الطعن في النسب، والنياحة على الميت.
Muslim narrated it in the Book of Faith (67) through several routes from Amash, from Abu Salih, from Abu Hurairah, and mentioned it.Imam Ahmad narrated it (9574) from Yahya, from Ibn Ajlan, who said, "Saeed narrated to me, from Abu Hurairah, and I heard my father narrating from Abu Hurairah" (the speaker here is Ibn Ajlan, that is, Muhammad). "I said to Yahya" (the speaker here is Imam Ahmad), "both of them from the Prophet ﷺ." He said, "Yes." He said, "Two traits from the affair of the Age of Ignorance that people will never abandon, wailing over the dead and defaming lineage." Its chain of transmission is sahih.Ibn Jarud narrated it (515) through another route from Abu Asim, from Ibn Ajlan, from his father, from Abu Hurairah, and mentioned it. This makes explicit what was left ambiguous in Ahmad's chain of transmission.