Be confident sleep is guaranteed (4,7)

I believe the answer is:

rest assured

'be confident' is the definition.
(thesaurus)

'sleep is guaranteed' is the wordplay.
'sleep' becomes 'rest' (synonyms).
'is guaranteed' becomes 'assured' (I've seen this in another clue).
'rest'+'assured'='REST ASSURED'

I've seen this clue in The Irish Independent and The Globe and Mail.

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