Do be quiet -- there's money (4)
I believe the answer is:
dosh
'money' is the definition.
(I've seen this before)
'do be quiet' is the wordplay.
'be quiet' becomes 'sh'.
'do'+'sh'='DOSH'
'there's' is the link.
(Other definitions for dosh that I've seen before include "Contents of purse" , "Bread - gravy - dough" , "Spondulicks" , "Moolah (slang)" , "Money (slang)" .)