Retire for the night (3,3,4)
I believe the answer is:
hit the sack
'retire for the night' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hit the sack that I've seen before include "Retired" , "went to bed" , "Drank a lot of vintage wine" , "retire" , "Turn in" .)