Tertullian

With regard also to the very dress and food, it commands (the penitent) to lie in sackcloth and ashes, to cover his body in mourning, to lay his spirit low in sorrows, to exchange for severe treatment the sins which he has committed; moreover, to know no food and drink but such as is plain,-not for the stomach's sake, to wit, but the soul's; for the most part, however, to feed prayers on fastings, to groan, to weep and make outcries unto the Lord your God; to bow before the feet of the presbyters, and kneel to God's dear ones; to enjoin on all the brethren to be ambassadors to bear his deprecatory supplication (before God).