/ban id [id] [time] [reason_using_underscores_instead_of_spaces]
I think.
To be able to use spaces in reasons, try this:
-Open console
-Type this:
commandToServer('ban', 0, BL_ID, time, "Reason");
Make sure to keep the 's around ban, and "s around your reason.
Using -1 for the time will make it perma.