Prohibition of Deriding one's Lineage and Bewailing the Deceased

Abu Hurairah (RA) said: The Messenger of Allah (PBUH) said, "Two matters are signs of disbelief on the part of those who indulge in them: Defaming and speaking evil of a person's lineage, and wailing over the dead."
[Muslim]

Commentary

Two sins mentioned in the Hadith are such that if a Muslim thinks them lawful and still commits them he will be not be integrated in the circle of Islam that he will be considered a kafir. The first sin is to defame someone's lineage means to disgrace or humiliate somebody by saying to him or to her: "Your father belongs to such and such profession" or "Your mother is such and such / so-and-so" or "You are a weaver, blacksmith, launderer, cobbler, etc.” Islam does not classify followers on the basis of race, color or cast. The status of a Muslim in the eyes of Allah is determined by the strength of faith, humbleness and piety. Therefore to speak evil of a person’s lineage and considering them from a lower category of human race is prohibited in Islam.

The second sin mentioned in the hadith is bewailing over the dead. It means weeping, crying and lamenting loudly over the deceased and expressing qualities and the problems that will arise due to his death. Such qualities are attributes and acts of the disbelievers and practices of the pre-Islamic period, or Jahiliyyah. Wailing causes trouble to the deceased in his grave as the hadith draw attention to it.

Umar bin Al-Khattab (RA) said: The Prophet (PBUH) said, "The deceased is tortured in his grave for bewailing over him.'' [Al-Bukhari and Muslim]