Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "a-býwan." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 5.
;p. de; pp. ed; v. trans. To adorn, purify, clarify; exomare, purgare :-- Beóþ monna gǽstas beorhte abýwde þurh bryne fýres the souls of men are brightly adorned [clarified] through the fire's heat, Exon. 63 b; Th. 234, 24; Ph. 545. v. býwan.