29 I entreat you, beloved brethren, that each one should confess his own sin, while he who has sinned is still in this world, while his confession may be received, while the satisfaction and remission made by the priests are pleasing to the Lord. Let us turn to the Lord with our whole heart, and, expressing our repentance for our sin with true grief, let us entreat God's mercy. Let our soul lie low before Him. Let our mourning atone to Him. Let all our hope lean upon Him. He Himself tells us in what manner we ought to ask. “Turn to me,” He says, “with all your heart, and at the same time with fasting, and with weeping, and with mourning; and rend your hearts, and not your garments.” Let us return to the Lord with our whole heart. Let us appease His wrath and indignation with fastings, with weeping, with mourning, as He Himself admonishes us.
Source: The Treatises of Cyprian (New Advent)