Atikṛccha (atikrichchha) is the name of a (purifying) ritual or vow (vrata) which requires to be observed over a stretch of twelve days. In order to observe this vow, the performer must obey certain rules of eating throughout the twelve-day long phase. For the first three days he should not eat anything but three handfuls before sunset; for the next three days he should not eat anything but the same three handfuls after sunset. For the third set of three days he would not eat anything but three handfuls of uncalled for food. And for the last three days he would fast. 

In Vaśiṣṭha Smṛti (Vasishtha Smriti) marks a difference between the vows kṛccha (krichchha) and atikṛccha. If the rule of three handfuls for the sets of three days in the manner mentioned above is observed, it is called kṛccha. Retaining the rule of the three days intact, if one eats only what one can consume at one gulp for the entire day, it is called the vow of atikṛccha. And when the handfuls of edible are replaced by gulps of water, but rest of the rue remains the same, the vow is called kṛcchātikṛccha. [Vashishtha Samhita (Aryashastra) 24.1-6]

Kullūkabhaṭṭa (Kullukabhatta), the annotator of Manusaṃhitā (Manusamhita), citing giants like Vaśiṣṭha (Vasishtha), Āpastamba (Apastamba) and Parāśara (Parasara), determined the stipulations of performing this vow in elaborate detail. While observing the vow of kṛccha [also called prājāpatya kṛccha (prajapatya krichchha)], one should eat twenty-two handfuls after sunset, twenty-six handfuls before sunset, and twenty-four handfuls from the uncalled for food; and the size of each handful would not exceed that of a fowl’s egg –

kukkuṭāṇḍa-parimāṇaṃ yāvāṃśca praviśenmukham
etadgrāsaṃ vijānīyāt śuddhyarthaṃ kāyaśodhanaṃ.