Ask about mission (7)

I believe the answer is:

request

'ask' is the definition.
('request' can be a synonym of 'ask')

'about mission' is the wordplay.
'about' becomes 're' (regarding).
'mission' becomes 'quest' (I've seen this before).
're'+'quest'='REQUEST'

(Other definitions for request that I've seen before include "bidding" , "Queer St (anag.)" , "Appeal" , "Ask for" , "Application" .)

I've seen this clue in The Telegraph.

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