The Animal That Takes Us to Nirvâna
322. Mules are good, if tamed, and noble Sindhu horses, and elephants with large tusks; but he who tames himself is better still.
323. For with these animals does no man reach the untrodden country (Nirvâna), where a tamed man goes on a tamed animal, viz. on his own well-tamed self.
Sacred Books of the East, Vol. 10: The Dhammapada and Sutta Nipata,
by Max Müller and Max Fausböll, [1881], at:
http://www.sacred-texts.com/bud/sbe10/sbe1025.htm