Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "ymb-sittan." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 753.
;p. -sæt, pl. -sǽton ; pp. -seten. I.to sit or be round, (1) to sit at table, meat, etc. :-- Ðæt hié mé þégon, symbel ymbsǽton, Beo. Th. 1132 ; B. 564. Hý twégen sceolon tæfle ymbsittan, Exon. Th. 345, 2; Gn. Ex. 182. Ða ymbsittendan circumsedentes, Bd. 4, 9; S. 577, 31: convivae, 5, 5 ; S. 618, 16: Ap. Th. 15, 6: 17, 4. (1 a) to sit at council, be engaged about :-- Hí án geþeaht ealle ymbsǽtan cogitaverunt consensum in unum, Ps. Th. 82, 5. (2) to be around, be neighbouring. v.