This is a principle affirmed by both the Sunnah and the consensus of the scholars, and it is likewise attested to in the Book of Allah. The Almighty says:

“Or do they have partners who have laid down for them in religion that for which Allah gave no permission?” (al-Shūrā 21).

Thus, anyone who urges an act by which one seeks closeness to Allah, or makes it obligatory—whether by word or deed—without Allah having legislated it, has instituted in the religion that which Allah has not authorized. Whoever then follows him in that has taken him as a partner with Allah, for he has legislated in religion what Allah did not permit.

True, such a person may have acted on an interpretation; if he exercised the level of ijtihād for which the erring mujtahid is pardoned, he will be forgiven and even rewarded for his effort. Nonetheless, it remains impermissible to follow him in that matter, just as it is impermissible to follow anyone whose statement or action is known to conflict with what is correct—even though the one who said or did it may be rewarded or excused.

Allah, Exalted be He, says:

“They took their rabbis and monks as lords besides Allah, and [also] the Messiah, son of Mary, while they were commanded to worship none but one God. There is no god but Him. Glory be to Him above what they associate with Him.” (al-Tawbah 31).

ʿAdiyy ibn Ḥātim said to the Prophet (peace and blessings be upon him): “O Messenger of Allah, they did not worship them.” He replied, “Indeed, they did not worship them; rather, they made lawful for them what Allah had forbidden and they obeyed them, and they forbade them what Allah had made lawful and they obeyed them.”

Therefore, whoever obeys another in matters of religion—whether in making something lawful or unlawful, or in deeming something recommended or obligatory—without Allah’s authorization, incurs a share of this censure, just as the one who commands or forbids incurs a share. Still, each of them may be excused for his ijtihād and even rewarded