Nasab is a fundamental concept in Islam that determines a child's relationship with the father, which then affects guardianship rights, inheritance, and family relationships. The preservation of lineage (hifz al-nasl) is one of the main objectives of Maqāṣid sharia because it has significant legal, social, and moral implications. Constitutio000nal Court Decision No. 46/PUU-VIII/2010 recognizes the civil relationship between an extramarital child and his biological father if it can be proven by technology or other valid evidence. This decision is in accordance with the concept of nasab in Islam but is not recorded by the state. This study examines the concept of nasab and the civil status of out-of-wedlock children in Constitutional Court Decision No. 46/PUU-VIII/2010 from the Maṣlaḥah perspective. Using a juridical-normative approach and descriptive analysis, this research is based on primary legal sources, including court decisions and legislation, as well as secondary literature discussing Maṣlaḥah. The results show that the decision is in line with the concept of Maṣlaḥah in Islam. The suitability of the Constitutional Court's decision with the concept of maslahah is based on the status of the applicant's marriage as religiously valid. Decision No. 46/PUU-VIII/2010 is not appropriate when used as jurisprudence for children born outside a legal marriage or can be called adulterous children.