Isnād

Chain of transmission — the unbroken chain of named narrators through which each hadith was passed from the Prophet's Companions through successive generations to the hadith compiler. Al-Nawawi verified the authenticity of each narration in the Arba'in, selecting only those of established reliability. The isnad is Islam's unique contribution to the science of historical verification: the names, characters, memories, and integrity of every person in the chain were scrutinised by specialists across centuries. No other civilisation developed a comparable system for preserving attributed speech — and the existence of the Arba'in as a reliable collection is a direct product of that system's rigour.

As understood in the classical tradition of Imam al-Nawawī and the scholars of his school.