These were the very last words Buddha spoke:
“Behold, O monks, this is my last advice to you. All component things in the world are changeable. They are not lasting. Work hard to gain your own salvation. Do your best.”
Then the Buddha lapsed into the Jhana stages or meditative absorption. Going from level to level, one after the other, ever deeper and deeper. Then he came out of the meditative absorption for the last time. After that he passed into Jhana a little way; and from this Jhana the Buddha passed into Nibbana leaving nothing whatever behind that can cause rebirth again in this or any other world.
The passing away of the Buddha occurred in 543 B.C. on a full-moon day in the month of May, known in the Indian calendar as Vesak.