Hanafi School:

• “As for the innovator, Abu Hanifa did not allow ‌prayer behind an innovator. Abu Yusuf said: ‘I dislike that the imam of the people be a person of innovation or desire.'” [Al-Ikhtiyar Li-Ta’leel Al-Mukhtar (1/58)]
• Al-Badr Al-Ayni said: “Muhammad narrated from Abu Hanifa and Abu Yusuf that ‌prayer behind people of desires is not permissible.” [Al-Binayah Sharh Al-Hidayah (2/333)]
• “According to Al-Hulwani, prayer is prohibited behind those who delve into speculative theology.” [Tabeen Al-Haqa’iq Sharh Kanz Al-Daqa’iq wa Hashiyat Al-Shalabi (1/135)]
• “In ‘Al-Mujtaba’ and ‘Al-Mabsut’: it is disliked to follow an innovator in prayer.” [Al-Binayah Sharh Al-Hidayah (2/333)]

Maliki School:

• “Malik said: Innovators should not be married, nor should one marry into their families, nor greet them, nor ‌pray ‌behind them, nor attend their funerals.” [Al-Mudawwanah (1/177)]
• Al-Abhari stated: “As for his dislike of praying behind the people of innovation, it is because they are not on the right path, and thus they should not be made imams to be followed. Don’t you see that it is disliked to ‌pray ‌behind a sinner? Similarly, the innovator is the same.” [Sharh Al-Mukhtasar Al-Kabeer by Al-Abhari (4/633)]
• Abu Al-Asbagh Al-Jiyani reported: “Whoever is known for some sectarian views contrary to the community, like the Ibadis, Murji’ah, Qadariyyah, or the like, one should not ‌pray ‌behind them or ‌behind a deviant imam. Whoever does pray behind them should repeat the prayer, whether in time or afterward, for the prayer is the head of the religion, and it deserves the utmost caution.” [Al-I’lam Bi Nawazil Al-Ahkam (p. 729)]
• Al-Qarafi said: “As for the people of innovation and desires, there is no distinction among their various ranks. Even if we permitted the leadership of sinners, we would prevent it for them, as it would proliferate innovation by making it prominent.” [Al-Dhakhirah by Al-Qarafi (2/240)]

Shafi’i School:

• Judge Husayn said: “The testimony of those who are not considered disbelievers from among the people of the Qibla, including those displaying innovation, is accepted, but ‌prayer behind them is disliked.” [Al-Ta’liqa by Judge Husayn (2/1031)]
• Al-Ruyani stated: “As for those openly promoting religious innovations, especially by criticizing the righteous predecessors, it is disliked to ‌pray behind them, but if one does, the prayer is valid since this does not expel them from Islam.” [Bahr Al-Madhhab by Al-Ruyani (2/263)]
• Al-Baghawi said: “It is permissible to ‌pray behind people of innovations and desires, but ‌prayer ‌behind ‌an innovator is more disliked than behind a sinner.” [Al-Tahdhib in Shafi’i Jurisprudence (2/269)]
• “Abu Ishaq said: Praying alone is better than praying ‌behind a Hanafi, and this is based on the validity of ‌prayer ‌behind a Hanafi.” [Rawdat Al-Talibin by Al-Nawawi (1/341)]
• Al-Nawawi stated: “It is disliked to ‌pray ‌behind a sinner and also ‌behind ‌an innovator whose innovation does not reach the level of disbelief. As for one whose innovation amounts to disbelief, it is not permissible to follow him.” [Rawdat Al-Talibin wa ‘Umdat Al-Muftin (1/355)]

Hanbali School:

• Imam Ahmad said: “‌One may ‌pray ‌behind a sinful person but not behind an innovator or a flagrant sinner, except if one fears them, in which case one should pray and then repeat the prayer.” [Al-Riwayatayn wa Al-Wajhayan – Fiqh Issues (1/172)]
• Harb Al-Karmani said: “The position of Abu Abdullah [Ahmad ibn Hanbal] is that ‌prayer should not be performed ‌behind innovators.” [Masail Harb Al-Karmani, Book of Purity and Prayer – Ed. Al-Sarie’ (p. 525)]
• Harb Al-Karmani also mentioned: “I do not like ‌prayer ‌behind the people of innovation, nor the funeral prayer over their deceased.” [Masail Harb Al-Karmani from the Book of Marriage to the End – Ed. Fayez Habis (3/971)]
• Ibn Qudamah said: “Whoever follows in prayer an imam who openly displays his innovation, speaks of it, calls to it, or debates on its behalf, must repeat the prayer … because the one who publicly displays his innovation leaves no excuse for the person praying ‌behind him.” [Al-Mughni by Ibn Qudamah (3/17)]