Is it permissible for the imam to tell those who are praying behind him to switch off their mobile phones when straightening the rows for the prayer?
Question

Despite the fact that there are signs reminding worshippers to switch off their mobile phones before entering the mosque, many of them forget to switch them off, which leads to disturbance for other worshippers, the imam and the owner of the phone himself. My question is: is it permissible for the imam to add a request to switch off mobile phones after telling the worshippers to complete and straighten the rows?
Praise be to Allah.We put this question to our shaykh, ‘Abd al-‘Azeez ar-Raajihi (may Allah preserve him) and he replied:
There is nothing wrong with him doing that, if he sees a need for it.
And Allah knows best.