In the Name of Allāh, the Ever Merciful, the Bestower of Mercy
al-Maqrīzī (رحمه الله) said:
“The root of every bidʿah (innovation) in the dīn (religion) is distancing oneself from the kalām (speech) of the salaf and deviating from the ʿaqīdah (creed) of aṣ-ṣadr al-awwal (the first generation [of Muslims]).”
Reference: al-Mawāʿiẓ wa-l-Iʿtibār bi-Dhikr al-Khiṭaṭ wa-l-Āthār.
Ibn Abī al-ʿIzz (رحمه الله) said:
“Rather, sūʾ al-fahm (misunderstanding) of Allāh and His Messenger (ﷺ) is the aṣl (root) of every bidʿah (innovation) and ḍalālah (misguidance) that has arisen in al-Islām, and it is the root of every khaṭāʾ (error) in both al-furūʿ (subsidiary matters) and al-uṣūl (foundational matters), especially if it is accompanied by sūʾ al-qaṣd (ill intent). Wa-Allāhu al-Mustaʿān (and Allah is the One whose help is sought).”
Reference: Sharḥ aṭ-Ṭaḥāwiyyah.
Translated by Abū Dilāra Naief al-ʿAydarūs.