From Polonius' speech to his son Laertes: (I'm not completely happy with the source I found on the web, but what can you do.)

...

Neither a borrower nor a lender be;
For loan oft loses both itself and friend,
And borrowing dulls the edge of husbandry.
This above all: to thine ownself be true,
And it must follow, as the night the day,
Thou canst not then be false to any man.