Cite the scanned version of the original dicionary like this:
Bosworth, Joseph. "fæsten-dæg." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth. Ed. Thomas Northcote Toller. Oxford: Clarendon Press, 1898. 267.
.Add: -- Gif hit fuguldæg sié ; gif hit festendæg sié C. D. i. 293, 10. Gif hit fæstendagas beón si jejunii dies fuerint, R. Ben. 67, 3. Gif wé on þǽm syx wucan fotlǽtaþ þá syx Sunnandagas þæs fæstennes (Lent), þonne ne bið þára fæstendaga ná má þonne syx and þrítig, Bl. H. 35, 24. On ðám fæstendagum in quibus diebus quadrigesimae, R. Ben. 74, 12. On eówrum fæstendagum in diebus jejuniorum vestrorum, Past. 315, 2. Þá fæstendagas þe men eów beódað tó healdenne, Wlfst. 230, 34. [v. N. E. D. fasten-day.] v.