Epictetus, Golden Sayings 100

In general, any methods of discipline applied to the body, which tend to modify its desires or repulsions, are good—for ascetic ends. 

But if done for display, they betray at once a man who keeps an eye on outward show, who has an ulterior purpose, and is looking for spectators to shout, "Oh what a great man!" 

This is why Apollonius so well said: "If you are bent upon a little private discipline, wait till you are choking with heat some day—then take a mouthful of cold water, and spit it out again, and tell no man!"