Qitzur Shulchan Arukh – 179:6
The borrower is prohbiited from taking the loan out for no need to the extent that it could get lost and the lender would find nothing from which to collect, even if the borrower is very wealthy. And whomever does so is called a “wicked person”, as it says, “The wicked borrow and do not pay, but the righteous deal graciously, and give.”
Our sages commanded, “Let your friend’s money be as dear to you as your own.”
When the lender recognizes the borrower, that he is someone of this attribute that he wouldn’t watch over others’ money, it is better not to lend him than to lend him and have to approach him afterward and violate each time “do not act toward him like a debt carrier” [see above, se’if 4].