The story
Mahāvīra gave his last teaching at Pāvāpurī in Bihar over two days without pause, and in the early hours of the new moon left the body and attained mokṣa, release from every rebirth. The eighteen kings who were listening lit lamps so that his light would not seem to have gone out; that, in the Jain telling, is why lamps are lit on this night.
His chief disciple Gautama Swāmī attained complete knowledge the same night, so the next dawn is kept as the first day of the year, and Jain merchants open their new account books on it.
