Green’s Dictionary of Slang

a dried bull’s penis, esp. when used as a whip.

1811		Lex. Balatronicum n.p.: Hung Beef. A dried bull’s pizzle. How the dubber served the cull with hung beef; how the turnkey beat the fellow with a bull’s pizzle.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.