Is prayer valid behind an Imam who, out of ignorance of its obligation, omits or violates a duty or condition of prayer, knowing that this duty or condition is a matter of scholarly disagreement, and does this take the same ruling as the emulation of one madhhab by another?

If an Imam fails to observe a pillar or condition of prayer due to ignorance, without any specific interpretation or adherence to a particular school of thought—for example, by omitting طمأنينة (tranquility)—some scholars hold that his prayer and the prayer of those who followed him are null and void. However, Ibn Taymiyyah favored the view that his prayer is valid, and if the Imam’s prayer is valid, then the prayer of those behind him is also valid.

If an Imam omits a disputed obligation without adherence to a specific school of thought or interpretation—such as the takbirat al-intiqal (transitional takbirs)—he is considered like one who forgets, and he must perform the prostration of forgetfulness (sujud as-sahw). If he omits it, his prayer and the prayer of the congregants remain valid.

This differs from followers of different madhahib (schools of thought) praying behind one another. In such cases, the prayer of both the Imam and the congregant is valid because the Imam’s belief is accounted for, and because the Companions and the Tabi‘un used to pray behind one another despite their differences in subsidiary matters.

It is obligatory for a Muslim to learn the individual obligations (fard al-ayn) such as purification (tahara) and prayer (salat).