How can falsification of Nasab (lineage) نسب be kufr?

Here it says that preservation of Nasab نسب (lineage) is one of the major goals, Maqasid al-Shariah مقاصد الشريعة of Islamic law and that falsification of lineage can be not only a major sin but kufra: > Lineage (Nasab) is a foundational element of human identity and a > crucial aspect of Islamic teachings, deeply intertwined with family > structures, inheritance rights, and societal order. Islam places > immense emphasis on preserving lineage, considering it one of the five > fundamental objectives of Islamic law (Maqasid al-Shariah). The Holy > Quran and Hadith explicitly prohibit altering, concealing, or falsely > attributing lineage, classifying such acts as major sins (kabira) and, > in some cases, as acts of disbelief (kufr) when committed > intentionally. This study explores the legal, moral, and social > dimensions of lineage in Islam, analyzing the severe consequences for > those who falsify their ancestry. > > Islamic law establishes clear guidelines regarding lineage to ensure > justice in inheritance, prevent confusion in kinship, and maintain the > sanctity of marriage prohibitions (mahram relationships). The Quranic > command "Call them by (the names of) their fathers; that is more just > in the sight of Allah" (Surah Al-Ahzab 33:5) serves as a divine > directive to uphold the integrity of lineage. Prophetic traditions > reinforce this by warning that falsely claiming another lineage > invites divine curses, social rejection, and severe punishments, > including exclusion from Paradise. Scholars from various Islamic > schools of thought have consistently affirmed that altering lineage > disrupts familial responsibilities, weakens social bonds, and leads to > moral and legal complications. > > Furthermore, this paper highlights the negative societal impacts of > lineage falsification, such as identity crises, psychological > distress, disputes over inheritance, and the risk of incestuous > relationships due to a lack of clarity in family ties. The study also > examines historical and contemporary interpretations of > lineage-related rulings, emphasizing the necessity of honesty in > lineage attribution to preserve familial harmony and societal trust. > > This research synthesizes Islamic jurisprudence, Quranic exegesis, and > Hadith analysis to conclude that safeguarding lineage is a religious > obligation and a critical measure for maintaining social justice, > legal clarity, and ethical order. Any deviation from truthful lineage > attribution is deemed a grave violation of Islamic principles, > warranting serious spiritual, social, and legal repercussions. How can falsifying lineage be kufr?