Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "mæst-ling." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 629.
, mæsling, mæslen [n], es; n.I.A kind of brass. The word is used to gloss aes, aurichalcum, and electrum :-- Mæstlingc ǽr and tin aurichalcum, aes et stannum, Coll. Monast. Th. 27, 11. Mæstlinc, gréne át auricalcos. Wrt. Voc. 286, 66. Cwicseolfer vel mæstling electrum i. sucus arboris, ii. 142, 78. Mæslen aes. Mk. Skt. Lind. Rush. 6, 8. Ðæt mæslenn (mæslen, Rush. ), 12, 41. Mæslen, Jn. Skt. Lind. Rush. 2, 15. II. a vessel made of the metal (? v. Halliw.