Sealed instruction for some severe brothers (8,5)

I believe the answer is:

enclosed order

'some severe brothers' is the definition.
(strict order of monks)

'sealed instruction' is the wordplay.
'sealed' becomes 'enclosed'.
'instruction' becomes 'order' (an order to do something).
'enclosed'+'order'='ENCLOSED ORDER'

'for' acts as a link.

I've seen this clue in The Guardian.

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