Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "þearfian." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 728.
;p. ode To be in need :-- Hé þearfigendra sáwla gehǽleþ animas pauperum salvos faciet, Ps. Th. 71, 13. [Icel. þarfa; p. parfaði.] v. be-þearfaþ, ge-þearfian; þearfan.