ثنتان في الناس هما بهم كفر: الطعن في الأنساب والنياحة على الميت
صحيح … [حم, م] عن أبي هريرة. شرح الطحاوية 377 مختصر مسلم55
It is reported that the Messenger of Allah (peace and blessings of Allaah be upon him) said:
“Two (deeds done) by the people are (a sign of) their disbelief: slandering one’s lineage and loud lamentations for the deceased.” 
This hadith was narrated by Ahmad (2/496) and Muslim (67) from the words of Abu Hurayra, may Allah be pleased with him.
The hadith is authentic. See Sahih al-Jami ‘as-saghir (138), Sharh at-takhaviyya (377), Mukhtasar Muslim (55).
These traits, which are manifestations of unbelief, remain from the era of Jahiliyyah. They are in people all the time, and only the one who was delivered from them by Allah Almighty, endowed with knowledge and faith, is freed from them. However, not everyone who displays one trait of unbelief becomes absolute unbeliever, just as not everyone who has one trait of faith becomes a true believer.
It can be seen from the hadith that patience is a mandatory religious prescription, and that unbelief also includes that which does not lead a person out of the Muslim community. See Fath al-Majid ‘Abdu-r-Rahman ibn Hasan.
 It means either that such deeds and manners are inherent in the unbelievers, or that they can lead a person to unbelief.