Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "mæsse-bóc." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 628.
;gen. -béc; f. A mass-book, missal :-- Saltere and pistol*-*bóc, godspellbóc and mæssebóc, sangbóc and handbóc, gerím and pastoralem, penitentialem and rǽdingbóc, ðás béc sceal mæssepreóst néde habban, L. Ælfc. C. 21; Th. ii. 350, 13: Chart. Th. 430, 7. On ðǽm ealdan sacramentorium, ðæt is on ðǽm ealdan mæssebócum, Shrn. 88, 5. [Orm. Havel. messe-bok: O. H. Ger. missi-puoh missalis: Icel. messu-bók.]