Two (things) are found among men which are tantamount to unbelief: slandering one's lineage and lamentation on the dead.  

قَالَ رَسُولُ اللَّهِ ﷺ اثْنَتَانِ فِي النَّاسِ هُمَا بِهِمْ كُفْرٌ الطَّعْنُ فِي النَّسَبِ وَالنِّيَاحَةُ عَلَى الْمَيِّتِ