
“In every age and clime we see
Two of a trade can never agree.”
Fable XXI, "The Rat-catcher and Cats". Comparable to: "Potter is jealous of potter, and craftsman of craftsman; and poor man has a grudge against poor man, and poet against poet", Hesiod, Works and Days, 24; "Le potier au potier porte envie" (translated: "The potter envies the potter"), Bohn, Handbook of Proverbs; also in Arthur Murphy, The Apprentice, act iii
Fables (1727)