Others have talked about the historical linguistics of _be_ in this phrase. On its use(s) as a set phrase, if you're interested in authoritative datings, a good list to ask would be the American Dialect Society List.
http://linguistlist.org/lists/get-list-detail.cfm?List=1
Most of what's done on there is lexicographical, and in particular one of the members is the editor of the _Yale Book of Quotations_, usually considered authoritative in these matters, I understand. So maybe try that book (or similar) first, and then ask the list.
All the best
Damien
--
Damien Hall
Newcastle University (UK)
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