It was during an Il Poya Day that Maithri Bodhisatva received Niyatha Vivarana from Gauthama Buddha. After receiving a robe from the Bodhisatva, the Buddha announced he will become the enlightened one during the eon of the 'Badra Kalpa'.
According to Buddhist history, is also on an Il Poya that the first Buddhist Missionary activity by the Sixty Arahath commenced, the 3 Jatila brothers entered the Buddhist order, Festival of "Devaharohana" or Ascend to heaven by Gautama Buddha and the day that chief disciple - Sariputta Maha Rahathan Thera passed away.
Sri Lankan Buddhists also commemorate Il Poya as the "Cheevara Masaya." The offering of "Katina Cheevaraya" is considered as a highly meritorious act, which take place in most of the Temples during the month of Il. The Katina Cheevara is brought to their respective temples in processions and offered to the resident Upasampada monks, who observed Vas. (Rainy Retreat) for nearly three months.
Furthermore, the enshrining of the right collar-bone of the Gautama Buddha's in the Thuparama Chaitya, which was constructed by 'King Devanampiyatissa', also took place on an Il Poya day.