Matsya Purana 50.63

50.63

kṣatrasyayājinaḥ kecit śāpāttasya mahātmanaḥ.
paurṇamāsena haviṣā iṣṭvā tasmin prajāpatim..
sa vaiśampāyane naiva praviśan vāritastataḥ.. 50.62 ..

When, after finishing the sacrifice of Prajâpati, on a full-moon day, Janamejaya was entering the hall of Sacrifice, he was prevented from doing so, by Vaiśampâyana, but the former did not heed him. On the contrary, Janamejaya, the son of Parîkṣit, after performing two Aśvamedha sacrifices, became a great Vâjasaneyaka, and went to the forest on account of his being cursed for entering into hostility with the Brâhmaṇas.—62-64.