Narrated by the Mother of the Believers, the Mother of ʿAbdullāh, ʿĀ’ishah [may Allāh be pleased with her] said: the Messenger of Allāh [ﷺ] said: ‘Whoever innovated in our matter [of Islam] that which is not from it will have [what he innovated] rejected.’¹ Narrated by Bukhārī and Muslim. In the narration of Muslim: ‘Whoever executes an action [in Islām] that is not from it will have [that action] rejected.’

Imām Ibn Rajab [d. 795 AH] said:
“This ḥadīth is from among the greatest foundations of Islām. For it behaves as a scale that applies to the outward appearance of all actions, just as the ḥadīth that all actions are judged by intention is a scale for the inward aspect of action. So just as any action not intended for the Face of Allāh the Most High holds no reward for the one carrying out that action, thus any action not supported by the command of Allāh and His Messenger [may the peace and blessings of Allāh be upon him] will be rejected. [That is because] anything that is innovated in this religion has not been granted permission by Allāh. As such, [such actions] have absolutely no place in this religion.”

Endnotes:
1. Bukhārī 5:301, Muslim 3:1343,1344.

Source: Jamiʿ al-ʿUlūm: 183
Translated by: Riyāḍ al-Kanadī