Call it a night (4,2)
I believe the answer is:
turn in
'call it a night' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for turn in that I've seen before include "Hand over - retire" , "Informally, go to bed or hand over" , "Hit the hay" , "Go to bed (informal)" , "Surrender" .)