قَالَ عَبْدَ اللَّهِ بْنَ الْمُبَارَكِ رَحِمَهُ اللَّهُ: الْإِسْنَادُ مِنَ الدِّينِ، وَلَوْلَا الْإِسْنَادُ لَقَالَ مَنْ شَاءَ مَا شَاءَ

‘Abdullāh bin Mubārak (may Allāh have mercy upon him) said:

“The isnād (chain of narration) is part of the dīn. If it were not for the isnād, then any person would have said (about Islām) whatever he wished.”

• Ṣaḥīḥ Muslim (Introduction, no. 31)
• Al-Jāmi’ li-Akhlāq ar-Rāwī wa-Ādāb as-Sāmi’ (1611 (2/200) – Published by Maktabah al-Ma’ārif, Research by Dr. Maḥmūd aṭ-Ṭaḥān with a slightly different wording in a longer narration.