Is it permissible to pray behind an imam from another madhhab (school of thought)?

There is no objection to performing congregational prayer behind an imam who belongs to a different madhhab. The difference in madhhab does not prevent following an imam in prayer. Although there is a juristic opinion stating, "If an imam from another madhhab does something during the prayer that would invalidate the prayer according to the follower's madhhab, the follower's prayer becomes invalid" (al-Fatāwā al-Hindiyya, 1/84; Ibn Abidin, Radd al-Muhtār, 1/562-563), the more correct approach is that as long as the imam's prayer is not invalid according to his own madhhab, the prayer of the one following him is also valid, regardless of the madhhab.

This latter view is in accordance with the practices of the early generations (salaf) and is also compatible with the spirit of congregational worship. For example, Imam Abu Yusuf prayed behind Caliph Harun Rashid, who led the prayer without performing ablution after cupping (hijama), even though this would normally require ablution. (Ibn Abil-‘Izz, Sharh al-‘Aqida al-Tahawiyya, 368-369) Furthermore, it is not necessary to investigate whether the imam has acted contrary to the conditions of his own madhhab. (Ibn Abidin, Radd al-Muhtār 1/562-563)

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu