Free advice lands a source of riches (8,4)
I believe the answer is:
aladdins cave
'source of riches' is the definition.
'free advice lands a' is the wordplay.
'free' is an anagram indicator.
'advice'+'lands'+'a'='advicelandsa'
'advicelandsa' anagrammed gives 'ALADDINS CAVE'.
(Other definitions for aladdins cave that I've seen before include "Source of treasure" , "Place containing fabulous riches" , "Treasury" , "treasure store" , "Place filled with treasures" .)