Rely on New Testament as money-related document (4,9)
I believe the answer is:
bank statement
'money-related document' is the definition.
'rely on new testament' is the wordplay.
'rely' becomes 'bank'.
'on' says to put letters next to each other.
'new' indicates anagramming the letters.
'testament' with letters rearranged gives 'statement'.
'bank'+'statement'='BANK STATEMENT'
'as' is the link.
(Other definitions for bank statement that I've seen before include "Record of financial transactions" , "Listing for balance" , "note of available funds" , "showing an indication of interest?" , "Printed facts and figures" .)