Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "eald-gestreón." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 166.
, es: n. An old treasure; antīquus thēsaurus :-- Ic ðé ða fǽhðe leánige ealdgestreónum I will recompense thee for the strife with old treasures, Beo. Th. 2766; B. 1381: Beo. Th. 2921; B. 1458: Exon. 31 a; Th. 96, 8; Cri. 1571.