Is it obligatory for those praying behind the imam to follow him if he prays with his arms at his sides (sadl) while they pray with their hands clasped (qabd)? And does anything result from their prayer behind an imam who prays with sadl? What is the ruling if the young people sit in the resting posture (jalsat al-istiraḥah) before rising from prostration while the imam does not do so?

It is sunnah for one praying behind an imam who dangles his hands to place his hands on his chest. It is also sunnah for him to observe the sitting of rest (jalsat al-istirahah) unconditionally according to the Shafi'is, because they exempted the sitting of rest from the obligation of following the imam, as it is a slight sitting. Therefore, there is no blame on these young men for differing from their imam in these matters, and each will be rewarded for his ijtihad (independent reasoning) or taqlid (following a qualified scholar).