How does that expression go?

[Peter9]

I'm not sure this is the right place to be asking, but I'm trying to find an expression. I'm not sure how it goes exactly.

I'm here for a [something] not a while
or,
I'm here for a while not a [something]

'while' and the other word probably rhyme. I thought smile, but I don't know. I might be completely off the mark with the whole thing.

[Mister Micawber]

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All I can think of is 'here for awhile but not for a long while'. I suppose that's not it, eh?
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Native English teacher at Mister Micawber's