Cite the scanned version of the original dicionary like this:
Bosworth, Joseph. "lár-bóc." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth. Ed. Thomas Northcote Toller. Oxford: Clarendon Press, 1898. 621.
.Add :-- Hé áwearp his lárbóc he flung away the book he was learning from, Hml. S. 4, 189. Paulus cwæð on his lárbócum (in his epistles), Hml. A. 77, 108.