What is the ruling on one who doubts a fard (obligatory act) while praying behind an Imam, such as al-Fatihah, or bowing (ruku'), or prostrating (sujood), especially when experiencing absentmindedness or distraction, and this occurs repeatedly twice or more daily?

Whoever doubts having omitted pillars while praying behind the Imam, if this doubt is not persistent but rather results from a lack of focus, then he must feel as if he is standing before God to avoid distraction. If he is unable to perform what he doubted omitting behind the Imam, he should perform one rak'ah after the Imam's salam, and there is no prostration of forgetfulness (sujud al-sahw) required of him according to the Maliki, Shafi'i, and Hanafi schools. However, if the doubt is persistent, he must continue following the Imam and disregard these intrusive thoughts. He is not required to perform the prostration of forgetfulness after the salam because he is a follower (ma'mum); the Imam's prostration of forgetfulness suffices for that of the follower.