Qur’ān al-Karīm:
قَدْ أَفْلَحَ ٱلْمُؤْمِنُونَ ٱلَّذِينَ هُمْ فِي صَلاَتِهِمْ خَاشِعُون َوَٱلَّذِينَ هُمْ عَنِ ٱللَّغْوِ مُّعْرِضُونَ
Successful indeed are the believers. Those who humbly cry in their prayers. And who do not incline towards indecent matters.
[Surah al-Mu’minīn, Verse 1-3] 

Tafsīr [exegesis] of the aforementioned verse:
Those who fear of offending Allāh Almighty must keep their parts of the body quiescent. Some Tafsīr experts opined that the expression of fear of Allāh Almighty by the performer of salāh should be in the following manner:-

1. Should be thoroughly absorbed in his salāh
2. Should withdraw his mind from worldly matters
3. Should save oneself from activities of sinful obedience to Allāh Almighty, for instance:
· Should not sight out of the prayer mat
· Should not indulge in useless acts or movements
· Should not hang both ends of cloth from his shoulder
· Should not indulge in finger crackling
· Should not look skywards[1]
[1] Tafsīr Khazain Ul-Irfān, pg 615