What is the ruling regarding an Imam forgetting a pillar or a condition, and what is the ruling regarding him doing so intentionally?

If the Imam deliberately omits a pillar of prayer, his prayer becomes invalid, and the prayer of those who followed him, knowing his condition, also becomes invalid. In this case, the follower must separate from him and complete his prayer individually. However, if the Imam omits a pillar forgetfully, he should be alerted by tasbeeh (saying "Subhan Allah"). If he does not understand, it is permissible to alert him by reciting from the Quran with the intention of recitation, such as: {So prostrate to Allah and worship [Him]} (Quran 53:62), or by supplicating, addressing Allah and not a created being, such as: "O Allah, remind him of such-and-such." If he still does not understand, it is permissible to alert him by speaking for the benefit of the prayer, such as saying: "the Tashahhud (definition)." If the Imam responds, then all is well. But if he does not respond, the follower must separate from him and complete the prayer individually, and the Imam must perform the prostration of forgetfulness (sujud (definition) al-sahw). As for forgetting a condition of prayer, its ruling varies depending on the condition.