Saw bovine comment about non-drinker (5)
I believe the answer is:
motto
'saw' is the definition.
(saw can mean a proverb or saying)
'bovine comment about non-drinker' is the wordplay.
'bovine comment' becomes 'moo' (I've seen this in another clue).
'about' indicates putting letters inside.
'non drinker' becomes 'tt' (Teetotaller abbreviation).
'moo' enclosing 'tt' is 'MOTTO'.
(Other definitions for motto that I've seen before include "Repeated theme in music" , "Words often found on coat of arms" , "Favourite saying of a group" , "device" , "Slogan encapsulating self-image" .)