What is the ruling regarding past prayers for someone who was unaware of the obligation of tranquility in them, then forgot that after coming to know of it, and is he excused by ignorance and forgetfulness?

Tranquility is a pillar of prayer according to the majority of scholars. It is achieved by the stillness of the limbs, even for a short time. Some have defined its duration as the time it takes to say "Subhan Allah" (Glory be to Allah). Whoever performs it, their prayer is valid and they do not need to repeat it. But whoever fails to observe it, their prayer is not valid, and they must make it up according to the majority of scholars until their obligation is fulfilled. However, according to the madhhab (school of thought) of Sheikh Al-Islam Ibn Taymiyyah and those who agree with him, there is no need for them to make it up, and they are excused due to ignorance.