There will be no unity nor power for the Muslims unless they return to acting in accordance with the Book of Allāh and Sunnah of His Messenger (صلى الله عليه وسلم) while abandoning whatever opposes it, especially as it relates to fundamental matters of creed. Allāh says:

وَاعْتَصِمُوا بِحَبْلِ اللَّهِ جَمِيعًا وَلَا تَفَرَّقُوا

“Hold fast to the rope of Allāh, altogether, and be not divided among yourselves.”
(Āl-ʿImrān, 3:103)

Truly, the latter generations of this ummah will not be rectified except by that which rectified its earlier generations [i.e., acting in accordance with the Qurʾān and Sunnah].

Source: Al-Irshād ilá Ṣaḥīḥ al-Iʿtiqād: 7
Translated by: Omar ibn Bilal