The World Federation One Stop Fiqh

Ruling 1117

If a person turns only his face away from qibla and his body remains facing qibla, in the event that he turns his neck to such an extent that he can see a little of what is behind him, the rule of turning away from qibla which was mentioned earlier – applies. However, if his turning is not to this extent but is commonly considered a lot, then based on obligatory precaution, he must perform his prayer again. If he turns his neck a little, his prayer does not become invalid, although this action is disapproved.