Allāh said:

فَإِن تَنَازَعْتُمْ فِي شَيْءٍ فَرُدُّوهُ إِلَى اللَّهِ وَالرَّسُولِ

“And if you disagree among yourselves over anything, then refer it back to Allāh and the Messenger.
(Al-Nisāʾ, 4:59)

Ibn Kathīr comments:

Mujāhid and others amongst the pious predecessors said: “That is, refer the matter of difference back to the Book of Allāh and the Sunnah of His Messenger (صلى الله عليه وسلم).” This is a command from Allāh—the Exalted in Might—to refer every matter of difference —whether they pertain to the fundamental creed of the religion or its subsidiary acts—back to the Book of Allāh and the Sunnah, as the the Most High said:

وَمَا اخْتَلَفْتُمْ فِيهِ مِن شَيْءٍ فَحُكْمُهُ إِلَى اللَّهِ

“And in whatsoever you differ, the decision thereof is with Allāh”.
(Al-Shūrā, 42:10)

Thus, whatever shows congruence with the contents of the Book of Allāh and the Sunnah represents the truth. So after the truth, what else can there be, save error?”

Source: Tafsīr Ibn Kathīr 3: 150.
Translated by: Omar Ibn Bilal