Serve a prison sentence (2,4)
I believe the answer is:
do time
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">serve a prison sentence</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for do time that I've seen before include "Serve a prison sentence" , "Serve porridge" .)