Neither a Borrower Nor a Lender Be

This was a difficult one for me over time, because I had so many people use it in my presence while I grew up.  My mother used to say it regularly, especially if I wanted an advance on my allowance.  She didn't have any idea where it came from though; she always assumed it was "just one of those things" passed down from generation to generation.  I had also heard that the phrase came from somewhere in the bible, but re-reading that was just too much to ask (once was enough, given that it took me 8 months to do the first time!).  Ultimately, it was my need to reference my complete volume of Shakespeare that led me to the result:

"Neither a borrower nor a lender be;
For loan oft loses both itself and friend,
And borrowing dulls the edge of husbandry."
William Shakespeare, Hamlet

Quod erat demonstrandum.

BTW: I won't tell you the exact location; I believe the works of Shakespeare to be pure gold, and well worth reading. Find it yourself, and enjoy the effort.