Patient man’s line of business (3)
I believe the answer is:
job
This clue is a triple definition!
'patient man's' is the first definition.
(biblical figure famous for patience)
'line' is the second definition.
(as in a person's line of work)
'of' acts as a link.
'business' is the third definition.
(I know that business can be written as job)
(Other definitions for job that I've seen before include "Assignment" , "Book; task" , "Personification of patience" , "Line" , "Task; paid position" .)