Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "gang-dagas." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 765.
, gong-dagas; pl. m. [dæg a day] Perambulation days, the three days before Ascension day or Holy Thursday, Rogation days, when the boundaries of parishes and districts were traversed; dies perambŭlātiōnes vel processiōnis, rogātiōnum dies :-- Betweox gang-dagum and middum sumera betwixt Rogation days and Midsummer, Chr. 913; Erl. 102, 3 : 1063; Erl. 195, 7. Ofer gang-dagas after Rogation days, L. Ath. i. 13; Th. i. 206, 15. Ðys Gódspel sceal to Gang-dagon this Gospel must be on the Rogation days [Gang-days], Rubc. Mt. Bos.