Matsya Purana 50.64

50.64

parikṣitaḥ sutaḥ so vai pauravo janamejayaḥ.
dviraśvamedhamāhṛtya mahāvājasaneyakaḥ.. 50.63 ..

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.