Write saying Gold is stocked by a pub West of Exmoor (8)

'write saying' is the definition.

'gold is stocked by a pub west of exmoor' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'stocked by' means one lot of letters goes inside another.
'pub' becomes 'ph' (public house).
'west of' indicates taking the first letters (most west - leftmost - letter).
The first letter of 'exmoor' is 'e'.
'or'+'is'='oris'
'a'+'ph'+'e'='aphe'
'oris' inserted inside 'aphe' is 'APHORISE'.