The Quran explicitly underscores the sanctity and importance of nasab, presenting it as a principle vital for human dignity and societal harmony. A key directive states, “Call them by their true fathers; that is more just in the sight of Allah”. This verse highlights the paramount importance of acknowledging biological paternity, emphasizing truthfulness and justice in attributing parentage. It serves as a foundational command against false claims or the deliberate obfuscation of lineage, ensuring that individuals are identified with their rightful ancestors. This divine command also resonates with the broader Quranic principle that We have created you from male and female and made you peoples and tribes that you may know one another, implying that understanding one's lineage is integral to self-identity and recognizing one's place within the wider human family. The legal ramifications of nasab — impacting inheritance, guardianship, and marriage prohibitions — are thus rooted in these explicit Quranic injunctions that prioritize clarity and justice.

Islamic law, particularly the Hanafi school, meticulously details the conditions under which paternity (nasab) is established, relying on presumptions that safeguard lineage. The primary principle is that paternity is typically established through a valid marriage or legal ownership, provided certain temporal conditions are met. For instance, the Hanafi school holds that [the period for establishing lineage is counted from the time of consummation, according to Muhammad, and this is the prevailing legal opinion (fatwa)]hidaya: vol 01 p209. This means that for a child to be attributed to a husband, the marriage must have been consummated.

Furthermore, specific gestation periods are crucial. If a wife gives birth, paternity is typically attributed to the husband if the birth occurs within certain minimum and maximum timeframes from the point of consummation or separation. For example, if a woman gives birth to a child [less than six months from the day he purchased her (after divorcing her), the child's lineage is attributed to him]hidaya: vol 02 p035. This establishes a minimum period for pregnancy. Conversely, paternity is not established if [she gives birth exactly two years after the separation]hidaya: vol 02 p033, as the pregnancy is presumed to have occurred after the divorce. However, there are differing opinions on the maximum duration; according to Abu Yusuf, paternity can be established up to twenty-seven months, positing conception at the end of the waiting period followed by a maximum two-year pregnancy hidaya: vol 02 p033. These rulings demonstrate the careful consideration given to biological realities within legal frameworks to prevent the disruption of nasab.

Beyond the presumption arising from marriage, nasab can also be established through acknowledgment (iqrar bi al-nasab). This legal mechanism allows an individual to claim a child as their own. The Hanafi school outlines specific conditions for such an acknowledgment to be valid. Crucially, [it is a condition that he (the boy) has no known lineage]hidaya: vol 03 p189. This prevents an acknowledgment from disrupting an already established nasab. Furthermore, the acknowledged child's confirmation is generally a condition for the establishment of paternity hidaya: vol 03 p189.

The consequences of a valid acknowledgment are significant. For example, [if someone acknowledges a debt to a stranger and then says, 'He is my son,' his paternity is established from him, and his acknowledgment of the debt to him becomes void]hidaya: vol 03 p189, illustrating how paternity supersedes other legal claims. However, the scope of acknowledgment is not unlimited; [whoever acknowledges a lineage other than parents or children, such as a brother or paternal uncle, his acknowledgment of lineage is not accepted because it imposes lineage upon someone else]hidaya: vol 03 p190. Such acknowledgments require confirmation from those upon whom the lineage would be imposed hidaya: vol 03 p190. Similarly, a woman's acknowledgment of a child's paternity is generally not accepted if it implicates her husband, unless he confirms it or a midwife testifies to the birth hidaya: vol 03 p190. Yet, [if a woman is neither married nor in her waiting period, they (the scholars) said that lineage is established from her by her statement]hidaya: vol 03 p177, recognizing her direct knowledge in such circumstances.

Given the profound importance of nasab, Islamic law provides mechanisms for resolving doubts and disputes concerning paternity. In cases where the husband denies paternity (jihad al-wiladah), the Hanafi school rules that it [is established by the testimony of one woman who testifies to the birth]hidaya: vol 02 p034. This highlights the acceptance of specialized female testimony in matters related to childbirth. Furthermore, in situations where a man acknowledges a child but then denies him, [he must perform mutual imprecation (mula'anah)]hidaya: vol 02 p114. Mula'anah is a specific judicial process involving solemn oaths and curses exchanged by spouses, effectively dissolving the marriage and severing paternity if a husband accuses his wife of adultery and denies the child's lineage.

Disputes over gestation periods are also addressed; for instance, if a husband claims he married his wife four months ago and she claims six months, and she gives birth, [her word is accepted, and the child is his]hidaya: vol 02 p034, demonstrating a presumption in favor of the mother's account in some scenarios. The Hanafi school also acknowledges instances of "doubt" (shubha) in which [lineage is established... if the child is claimed]hidaya: vol 02 p099, further indicating a legal inclination to establish paternity where possible.

The legal landscape of nasab extends to various specific scenarios, including the children of slave-girls and foundlings, reflecting the comprehensive nature of Islamic law.

For children born to slave-girls, the Hanafi school outlines detailed rules. If a man has intercourse with his son's slave girl, and she gives birth, and he claims the child, [the child's lineage is established from him, and she becomes his Umm Walad (mother of his child)]hidaya: vol 02 p069. This status grants the mother certain protections, including freedom upon her master's death. However, this is constrained by guardianship; [if the paternal grandfather has intercourse (with a slave girl) while the father is still alive, the lineage (of the child) is not established from him because the grandfather has no guardianship (wilayah) as long as the father is alive]hidaya: vol 02 p069. This clarifies that legal guardianship dictates whose claim to paternity is valid. When the father is deceased, however, the lineage can be established from the grandfather hidaya: vol 02 p069. Complexities also arise if a pregnant slave girl is sold; generally, the seller's claim to paternity is preferred if the birth occurs within a reasonable timeframe (hidaya: vol 03 p174, 175).

Foundlings (laqit) are another category requiring specific legal provisions to establish their lineage and rights. A foundling is presumed free, and [if someone claims that a foundling is his slave, his claim is not accepted... unless he provides evidence]hidaya: vol 02 p173. This presumption safeguards the child's freedom. If a foundling is discovered in a Muslim city and [a Dhimmi claims him as his son, his lineage is established from the Dhimmi, and the child is considered Muslim]hidaya: vol 02 p173. This ruling is particularly significant, establishing paternity while simultaneously recognizing the child's default Muslim status in such an environment. Any property found with a foundling, such as money tied to them or to an animal they are riding, is considered to belong to the foundling hidaya: vol 02 p173.

The intricate rules surrounding nasab in Islamic law serve a greater purpose than mere genealogical record-keeping; they are integral to the ethical and social fabric of the Muslim community. By meticulously defining the establishment, acknowledgment, and protection of lineage, Islam ensures clarity in relationships, which is fundamental for upholding rights and responsibilities. This precision prevents ambiguity in matters of inheritance, guardianship, and permissible marriage, thereby maintaining the sanctity of family units. The emphasis on preserving true paternity protects individuals from misrepresentation, fosters a sense of belonging, and prevents social disorder. Ultimately, these legal provisions underscore a profound commitment to justice and the wise organization of human society, reflecting the divine directive to “call them by their true fathers; that is more just in the sight of Allah”. The comprehensive framework for nasab ensures that every individual's foundational identity is acknowledged and protected, reflecting the profound value Islam places on truth, justice, and familial integrity.