Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "Hám-tún." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 505.
[or Ham-tún?] Hampton, a common local name, used for both the present Northampton, Chr. 917, Erl. 102, 12; and Southampton, Chr. 981; Erl. 129, 36: for other towns see the index to Cod. Dipl. Kmbl. vol. vi.