Rambam - Sefer HaMitzvos: Negative Mitzvot 248, 249: Negative Mitzvot 248, 249

Negative Mitzvah 248: It is forbidden to deny our debts
Leviticus 19:11 "You shall not reply falsely"

We are not allowed to deny that we owe a debt to someone else and refuse to pay it. Additionally, we are forbidden to deny that someone has given us an object to keep in our care and watch for him.

Negative Mitzvah 249: It is forbidden to swear falsely about a debt
Leviticus 19:11 "Neither shall you lie to each other"

We are not allowed to swear that we do not owe debt when in fact, we do.

There are sparks of light hidden in this world. Some you can find and liberate: When you "Know G-d in all your ways", finding Him in whatever you do -- those sparks jump out at you and their light is released. But then there are sparks of such intensity that they needed to be buried in the deepest bowels of the material realm and locked away in thick darkness. These are sparks that no ordinary search could uncover: Your intellect has no power even to approach them. Your deeds could never dig that deep. Your eyes would be blinded by their brilliance and by the profundity of the darkness surrounding them.
The only tools you have to liberate those sparks are the ones that supersede your intellect and your senses. These are the inner powers that are revealed when you withstand a test of faith.
This is the reason we find our faith tested again and again in this generation: We are redeeming the final sparks of light.

From: Bringing Heaven Down to Earth by Tzvi Freeman - tzvif@aol.com