The correct placement of the hands when standing up after rukoo’ is to place the right hand on the left forearm, not to let the hands hang by the sides.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: it seems that the Sunnah is to place the right hand on the left forearm, because of the general meaning of the hadeeth of Sahl ibn Sa’d which was narrated by al-Bukhaari: “The people were commanded that a man should put his right hand on his left forearm when praying.” If you look at the general meaning of this hadeeth you will note that it says “when praying,” not “when standing”. Thus it will be clear that when standing after rukoo’ it is prescribed to put (the right hand on the left forearm), because when bowing (rukoo’) the hands are placed on the knees, and when prostrating they are placed on the ground, and when sitting they are placed on the thighs. But when standing – which includes standing both before and after rukoo’ – a person should place his right hand on his left forearm.
This is the correct view.
Al-Sharh al-Mumti’, 3/146.
And Allaah knows best.