• What happened: Lord Mahavira’s last sermon is known as the Uttarādhyāyana Sutra. He spoke continuously for about 48 hours at Pavapuri, then entered Parinirvāṇa (nirvana) the next morning. This event marks the end of his mortal body and the beginning of his Siddha (liberated) state. There are slight textual and dating differences between Śvetāmbara and Digambara traditions, but the sequence (last sermon lasting 48 hours, then Nirvana at Pavapuri) is common to both. ( jainknowledge.com)

• The date often given:

- Śvetāmbara tradition: Nirvāṇa on Kartik Śukla or Kartik Amāvāsya, commonly dated to 527 BCE. - Digambaras sometimes give a slightly different year (around 510 BCE). The place of Nirvāṇa is Pawapuri (Pavapuri) in present-day Bihar. ( jainknowledge.com)

• The connection to Diwali: Diwali in Jain practice commemorates Mahavira’s Nirvāṇa. The night of his last sermon, and the following early dawn when he attained liberation, are tied to the Diwali period in the Jain calendar. The day after is often treated as the Jain New Year (Gautam Swami’s Keval Jñāna) in many communities. ( jainknowledge.com)

• Core source name you may encounter: Uttarādhyāyana Sutra is the text of Mahavira’s final teachings. It is revered as his last sermon and is read/recited during Diwali celebrations among Jains. ( jainknowledge.com)

• Simple summary in one line: Mahavira gave his final, two-day discourse at Pavapuri, then, on the Kartik period, achieved nirvāṇa there; Diwali is celebrated as this Nirvāṇa Kalyanak. ( jainknowledge.com)

Read more (authentically presented in Jain Knowledge pages):

• You can read more about Mahavira’s last sermon and Nirvāṇa on Diwali here
• You can read about Diwali according to Jainism here
• You can read about Mahavira’s Nirvāṇa Kalyanak (Diwali) here