What is the ruling on one who contradicts the Imam in prayer, so he prostrated when the Imam bowed, and did not stand until after three prostrations in a single rak'ah?

The follower's adherence to the Imam in prayer is obligatory. Therefore, if someone omits bowing (rukūʿ) and completes the rakʿah with three prostrations, their rakʿah is invalid. They must perform another rakʿah after the Imam's salutation, and then perform the prostrations of forgetfulness (sujūd as-sahw).