What is the origin concerning prayer: is it letting the hands hang loose, or placing them on the chest, and why do some let their hands hang loose in prayer?

The majority of scholars hold that "qabd" (placing the right hand over the left) is a Sunnah, basing their argument on the actions of the Prophet, peace and blessings be upon him, who used to place his right hand over his left while standing in prayer. As for "sadl" (letting the hands hang by the sides), nothing authentic has been reported from him, peace and blessings be upon him, regarding it. Nevertheless, the Malikis adopted this view.