Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "ádl." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 755.
, ádel; g. ádle, f: ádle, an; f. A disease, pain, a languishing sickness, consumption; morbus, languor :-- Wæs seó ádl þearl, hát and heorogrim the disease was sharp, hot and very fierce, Exon. 47a; Th. 160, 30; Gú. 951. Seó mycle ádl the great disease, leprosy; elephantiasis, Som. Ne hine dréfeþ ádl disease does not afflict him, Beo. Th. 3476; B. 1736. Ðé to heortan hearde grípeþ ádl unlíðe fell disease gripes thee hard at heart, Cd. 43; Th. 57, 32; Gen. 937.