MN131 Bhaddekaratta Sutta, 'A Single Excellent Night'(Middle Length Discourses of the Buddha, translated by the Ven. Bhikkhus Naa.namoli and Bodhi):
"Let not a person revive the past
Or on the future build his hopes;
For the past has been left behind
And the future has not been reached.
Instead with insight let him see
Each presently arisen state;
Let him know that and be sure of it,
Today the effort must be made;
Tomorrow Death may come, who knows?
No bargain with Mortality
Can keep him and his hordes away,
But one who dwells thus ardently,
Relentlessly, by day, by night -
It is he, the Peaceful Sage has said,
Who has had a single excellent night."