The Buddha once noted:
They do not ever lament over thepast,
They do neither yearn for what has yet to come,
They maintain themselves in thepresent here & now,
therefore is their appearance so calm and serene!
Samyutta Nikaya I, 5

Let go of the past, let go of the future,
let go of the present, and cross over to the
further shore of all becoming and existence.
With mind wholly liberated and fully released,
you shall never come back to birth and death!
Dhammapada 348

The past should not be followed longing after
and the future neither desired nor urged for!
What is past, not real anymore, is dead & gone,
and the future, not real now, have yet to come!
Majjhima Nikaya III, 131