Cite the scanned version of the original dicionary like this:
Bosworth, Joseph. "a-beornan." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth. Ed. Thomas Northcote Toller. Oxford: Clarendon Press, 1898. 3.
(-bi(e)rnan). Add :-- Ábyrnð exardescit, Ps. L. 38, 4. Hé ábarn (exarsit) mid ðý bryne wælhreównesse, Gr. D. 162, 22. Ðæt his mód áburne (exardesceret), 337, 33. Áburnon exarserunt, Ps. L. 117, 12.