We hear Peg leaves for a drink (3)
I believe the answer is:
tea
'leaves for a drink' is the definition.
(tea leaves)
'we hear peg' is the wordplay.
'we hear' indicates a 'sounds like' (homophone) clue.
'peg' becomes 'tee' (tee is a kind of peg).
'tee' sounds like 'TEA'.
(Other definitions for tea that I've seen before include "Leaves for brewing" , "Assam, e.g." , "Popular drink" , "Meal/drink" , "Infused beverage" .)