How is it to reserve a place in the mosque?
Reserving a place in the mosque by placing one's handkerchief, cap, or prayer mat is Makruh, and in this case, that person will not be entitled to that place. Rather, whoever arrives first in the mosque and sits in a place is entitled to it. Yes, if a person worships for some time in a place in the mosque, then wants to leave for a short while due to some need, and reserves the place by placing a handkerchief etc., then this is permissible and he will be entitled to that place. (Aham Masail/Vol:2/Pg:187)