Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "sǽgan." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 692.
;p. de To cause to sink :-- Óþ ðæt seó sunne on súþrodor sǽged weorðeþ (cf. Só giségid wurð sedle náhor hédra sunna, Hel. 5715), Exon. 207, 15; Ph. 142. v. on-sǽgan; sígan.