What is the ruling on saying: "Let him eat the unlawful" out of anger at a debtor's procrastination, then paying off his debt and lying to my colleague that the debtor had paid it, thinking that lying is permissible for reconciliation?

The phrase "Let him eat the unlawful (haram)" when said about a wealthy person who delays repaying his debt is not considered prohibited backbiting (ghibah), based on the Prophet's (peace be upon him) saying: "The procrastination of the wealthy (debtor) makes his honor and punishment lawful." This means that the delay by a person of means permits speaking about him in a way that would otherwise not be permissible, were it not for his procrastination. As for the phrase "He repaid his debt," it is possible that this is an allusion to truthfulness without requiring that the debtor himself repaid his debt.