[Ruling on Praying Behind People of Corrupt Beliefs]

Answer (and Allah grants success): Whoever’s creed is sound in Divine Oneness, Divine Justice, Prophethood, and what pertains to these foundations of religion—the prayer is valid behind him if he is among the God-fearing.
As for one who holds corrupt beliefs, the prayer is not valid behind him—whether he folds his hands or not, and whether he says “āmīn” or not.
Likewise, the prayer is not valid behind one who brazenly defies Allah by sinning and persists in it, whether by neglecting an obligation or committing a prohibition.
As for folding the hands and saying āmīn themselves, they do not, in and of themselves, prevent praying behind one who does them and believes them to be lawful; however, they suggest that there may be corrupt beliefs behind them, since they have become emblems of the anthropomorphists (al-mushabbihah), the compulsionists/ predestinarians (al-mujabbirah), and the nāṣibīs. Therefore, a religiously observant person should not pray behind one who does them until it becomes clear that none of those deviant beliefs lie behind them.
It is stated in al-Majmūʿ: “One does not pray behind the Ḥarūriyyah (Kharijites), nor behind the Murjiʾah, nor the Qadariyyah, nor one who has taken up enmity against the family of Muḥammad—may Allah bless him and his family and grant them peace.”
And in the ḥadīth narrated from the Prophet—may Allah bless him and his family and grant them peace: “Let not a wicked man lead a believer, and a Bedouin lead a migrated (in prayer),” and from him: “Do not let one who is brazen in his religion lead you (in prayer).”
This is also supported by what Abū Dāwūd and Ibn Ḥibbān in his Ṣaḥīḥ narrated from Abū Sahlah, one of the Companions of the Prophet—may Allah bless him and his family and grant them peace —that a man led a people and spat toward the qiblah while the Messenger of Allah—may Allah bless him and his family and grant them peace—was looking on. When he finished, the Messenger of Allah—may Allah bless him and his family and grant them peace—said: “Let this man not lead you in prayer.” Later he wanted to lead them again, but they prevented him and told him what the Messenger of Allah—may Allah bless him and his family and grant them peace—had said. He mentioned that to the Messenger of Allah—may Allah bless him and his family and grant them peace—who replied, “Yes [that is so],” and (I think) he said, “You have offended Allah and His Messenger.”
A similar report is narrated by al-Ṭabarānī in al-Kabīr with a good chain, from ʿAbd Allāh b. ʿUmar, from the Prophet—may Allah bless him and his family and grant them peace. (As cited in a marginal note on al-Minḥah.)
As for what is reported from the Prophet—may Allah bless him and his family and grant them peace—that he said, “Pray behind every righteous and every wicked person,” and, “Pray behind whoever says ‘Lā ilāha illā Allāh.’” al-Jalāl said in Ḍawʾ an-Nahar: all of their routes are weak and unsound.
It is also known in the religion of Islam that the sinner (fāsiq) must be humiliated, boycotted, and treated with enmity until he repents and returns to Allah. Accordingly, it is impermissible to honor him and elevate him by appointing him to lead the prayer, since that contradicts what is known—namely, the duty to humiliate him and show enmity toward him.
As for Ibn al-Amīr’s statement that “Whoever’s prayer is valid for himself, his imamate is valid,” and his adducing as proof the texts encouraging congregation—that is incorrect, for the proofs we have presented; and it is refuted by counter-examples: a woman’s prayer is valid for herself, yet her imamate over men is not valid; and those who are seated, or using dry ablution (tayammum), or deficient in purification, or deficient in their prayer—their prayer is valid for themselves, yet their imamate is valid only over their likes, according to many scholars from the Prophet’s Household and others.
Moreover, the encouragement of congregation does not indicate the permissibility of praying behind transgressors.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1