Upon whom is the responsibility of paying blood money (Aql) incumbent?

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The responsibility for paying blood money is only incumbent upon those whose lineage (nasab) from the killer is known, or those known to belong to a group where responsibility is collectively assumed by all members. If the lineage is unknown, the responsibility does not fall upon them, even if they belong to the killer's tribe. For instance, if the killer is Qurayshi, the entirety of Quraysh is not obligated to pay, because their tribes have fragmented, and each group is distinguished by an immediate paternal ancestor. Liability is only binding upon those who share kinship to that immediate known ancestor. However, if the killer belongs to a specific branch (fakhidh) where it is established that all members bear the responsibility, then all members must pay, regardless of whether the specific lineage of the individual killer is known to them, due to the certainty of collective liability.