John Lightfoot on Matthew 9:9

[He saw a man sitting at the receipt of custom, called Matthew.] Five disciples of Christ are mentioned by the Talmudists, among whom Matthew seems to be named: "The Rabbins deliver, There were five disciples of Jesus, Mathai, Nakai, Nezer, and Boni, and Thodah." These, they relate, were led out and killed. See the place. Perhaps five are only mentioned by them, because five of the disciples were chiefly employed among the Jews in Judea: namely, Matthew who wrote his Gospel there, Peter, James, John, and Judas.

Matthew seems to have sat in the custom-house of Capernaum near the sea, to gather some certain toll or rate of those that sailed over. See Mark, chapter 2:13, 14.

"He that produceth paper [on the Sabbath] in which a publican's note is writ, and he that produceth a publican's note, is guilty." The Gloss is, "When any pays tribute to the lord of the river, or when he excuses him his tribute, he certifies the publican by a note [or some bill of free commerce], that he hath remitted him his duty: and it was customary in it to write two letters greater than ours." See also the Gemara there.