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.