Beware the ides of March....

Caesar:
Who is it in the press that calls on me?
I hear a tongue shriller than all the music
Cry "Caesar!" Speak, Caesar is turn'd to hear.


Soothsayer:
Beware the ides of March.


Caesar:
What man is that?


Brutus:
A soothsayer bids you beware the ides of March.


Julius Caesar Act 1, scene 2, 15–19

from enotes

(one of my favourite quotes others are "Alas, poor Yorick. I knew him well" and "Where is Polonius? Ah you can nose him up the stairs..." -- both from Hamlet)