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. Then He
passed into Jhana a little way; and from this Jhana He 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.