How can one repent from innovations (bidʻah) if it is not known which actions are innovative, and is there a supplication for protection from them, and what is the best way to advise those who commit them?

The danger of innovations (bid'ah) is immense, for they lead to misguidance and the Hellfire, and they cause division within the Ummah. The innovator considers himself to be doing good, so he does not repent. Furthermore, innovations waste the efforts of their practitioner, as he believes he is doing well, fulfilling the words of Allah Almighty: ﴿Say, "Shall We inform you of the greatest losers in [their] deeds? Those whose effort is lost in worldly life, while they think that they are doing good work."﴾

To avoid innovations: seek Islamic knowledge, shun the company of innovators and reading their books, frequently supplicate to Allah for guidance to the straight path, and be diligent in reciting prophetic supplications such as: «O Allah, guide me and grant me rectitude,» and «O Allah, I ask You for steadfastness in the matter and determination in guidance,» and engage in general repentance from sins.

As for condemning innovations, it is one of the greatest acts of proximity to Allah, fulfilling the words of Allah Almighty: ﴿And let there be [arising] from among you a nation inviting to [all that is] good, enjoining what is right and forbidding what is wrong, and those will be the successful.﴾ And according to the saying of the Prophet ﷺ: «Whoever among you sees an evil, let him change it with his hand; if he cannot, then with his tongue; if he cannot, then with his heart—and that is the weakest of faith.»

It is a condition for the one who condemns an evil that he has knowledge of what he is condemning, and that he is gentle in his advice, fulfilling the words of Allah Almighty: ﴿Invite to the way of your Lord with wisdom and good instruction, and argue with them in a way that is best.﴾ If the innovator seeks to spread his innovation, then it is best to avoid associating with him.