Agni Purana states that when an individual commits sins there are certain ways with the help of which those sins are atoned. Atonement of Sin according to the Agni Purana is very necessary. It has been stated that purification of the soul may come about by the performance of the sacrifice known; Gomedha or by repeating one of the four Vedas. The sinner can also go into a voluntary exile. It has been said that an intelligent penitent should duly put up the sacrificial fire, and cast into it libations of clarified butter in honour of the Moon, Indra, the Jupiter and the other gods.
A thief having stolen gold weighing more than thirty Ratis, should go to the king's court, and should confess his guilt, and ask the king to deal with him accordingly. A penance for the atonement of sins due to the murder of a Kshatriya, a Vaishya, or of a Shudra, should be respectively practised for a quarter, eighth and the sixteenth part of the period, laid down in the case of murdering a Brahmana. A man having killed a cat, a mongoose, a frog, a dog, a donkey, an owl, and a crow should practise the penance he ought to have done, if he had killed a Shudra. Similarly the same penance should be practised for atonement of the sin of accidentally killing a woman of whatever caste. A man having stolen any article of small value or substance from the house of another, should practise the penance known as the Krichchha Santapana, at the close of which he would be pure. The eating of Panchagavya should be deemed as the proper expiation of sin due to the stealing of edibles, fruits, flowers, roots, beddings or a litter from the house of another. The sin incidental to the stealing of hay, fuel, a tree, molasses, and dried rice should be atoned for by observing a fast for three days; while the period should be extended to twelve days, where the articles stolen would consist of gems, pearls, corals, copper, silver, iron, bell metal or stone, absolute fast being not necessary in the case of a man, who may live on a single grain of rice each day.
A man having stolen the rope or the halter of a mule or an ass which has become old and worm-eaten, or having taken away without the knowledge and consent of the owner, a bird, an article of perfume, or cereals, shall live on milk diet simply, for three consecutive days. A man having gone unto a woman, who is the wife of his own friend or any way related to him, or unto a sister of his own father or mother or having defiled a wife of his own father, or that of a man of a very low caste, should practise the penance known as the Gumtalpa Vrata.
Thus it is very evident from this chapter or Adhyaya of Agni Purana that it is needed that one undergoes atonement of the sin which he or she commits.