Stop painting, say, and begin again (7)
I believe the answer is:
restart
'begin again' is the definition.
('start' can be a synonym for 'begin' so perhaps 'restart' is OK for 'begin again')
'stop painting say' is the wordplay.
'stop' becomes 'rest' (to take a rest is to stop).
'painting say' becomes 'art' (painting is a kind of art).
'rest'+'art'='RESTART'
'and' acts as a link.
(Other definitions for restart that I've seen before include "Commence again" , "Begin anew" , "Jumping the gun will mean" , "launch again" , "Resume" .)