Vishnupurana 3.5.4

3.5.4

ṛṣir yo 'dya mahāmerau samājenāgamiṣyati
tasya vai saptarātrāt tu brahmahatyā bhaviṣyati //

It had been formerly agreed by the Munis, that any one of them who, at a certain time, did not join an assembly held on mount Meru should incur the guilt of killing a Brahman, within a period of seven nights. Vaiśampáyana alone failed to keep the appointment, and consequently killed, by an accidental kick with his foot, the child of his sister. He then addressed his scholars, and desired them to perform the penance expiatory of Brahmanicide on his behalf. Without any hesitation Yájnawalkya refused, and said, "How shall I engage in penance with these miserable and inefficient Brahmans?" On which his Guru, being incensed, commanded him to relinquish all that he had learnt from him. "You speak contemptuously," he observed, "of these young Brahmans, but of what use is a disciple who disobeys my commands?" "I spoke," replied Yájnawalkya, "in perfect faith; but as to what I have read from you, I have had enough: it is no more than this--" (acting as if he would eject it from his stomach); when he brought up the texts of the Yajush in substance stained with blood. He then departed. The other scholars of Vaiśampáyana, transforming themselves to partridges (Tittiri), picked up the texts which he had disgorged, and which from that circumstance were called Taittiríya; and the disciples were called the Charaka professors of the Yajush, from Charańa, 'going through' or 'performing' the expiatory rites enjoined by their master.