Devibhagavatapurana 11.23.34

11.23.34

svādhyāyābhyasanasyādau prājāpatyaṃ careddvijaḥ |
keśaśmaśrulomanakhān vāpayitvā tataḥ śuciḥ ||

One becomes freed of all the sins, if one performs the above five Chândrâyanas. By the performance of the Tapta Krichchhra, all sins are burnt off in an instant. By the performance of the three Chândrâyanas the people get purified and go to the Brahma Loka. By doing eight Chândrâyanas, one sees face to face one’s Devatâ, ready to grant boons. With ten Chândrâyanas, one gets the knowledge of the Vedas and one acquires all what one wants.
In the observance of the Krichchhra Prâjâpatya Vrata, one has to take food once in midday for three days, once in the evening for three days, and for the next three days whatever one gets without asking anything from anybody. For the next three days one is not to take any thing at all and go on with one’s work. These twelve days’ work constitutes the Prâjâpatya Vrata.
Now about the rules of the S’ântapana Vrata. On the preceding day one has got to eat food consisting of the mixture of cow urine, cow-dung milk, curd, ghee and the water of the Kus’a grass; the day following he is to fast. These two days’ work constitutes the S’ântapana Vrata.
Now about the Ati Krichchhra vrata. For the first three days, one is to eat one mouthful of food a day and for the next three days one is to fast. This is the Ati Krichchhra vrata. This vrata repeated three times is called Mahâ S’ântapana vrata. Note:-- According to the opinion of Yama, the fifteen days’ work constitutes Mahâ S’ântapana. For the three days one has to eat cow-urine; for the next three days, cow-dung, for the next three days, curd; for the next three days milk; and for the next three days one has to take ghee. Then one becomes pure. This is called the all sin-destroying Mahâ S’ântapan Vrata. Now I am speaking of the nature of the Tapta Krichchhra Vrata.
The Tapta Krichchhra vrata is carried out for the twelve days. For the first three days, one has to drink hot water; for the next three days, hot milk; for the next three days, the hot ghee and for the next three days, air only. Everyday one has to bathe once only under the above rules, and remain self-controlled. If one drinks water simply everyday under the above conditions, that is called the Prâjâpatya vrata.
To remain without any food for twelve days according to rules is called the Parâka Krichchhra vrata. By this vrata, all sins are destroyed.
Now about the rules of taking food in the Chândrâyana vrata. In the dark fortnight one will have to decrease one mouthful of food every day and in the bright fortnight one will have to increase one mouthful every day and one has to fast completely on the Amâvasyâ (new moon) day. One has to bathe thrice daily during every Sandhyâ time. This is known as the Chândrâyana Vrata.
In the S’is’u Chândrâyana Vrata one will have to take four mouthfuls of food in the midday and four mouthfuls in the evening. In the Yati Chândrâyana one has to take eight mouthfuls in the midday and to control his passions.