What is the ruling on a customer not paying their due installments in an installment sale, and is that considered charity to the merchant?

Selling on installment to help people is an act of leniency for which the seller is rewarded. The buyer must pay the price when the term is due if he is able; otherwise, he is sinful. The merchant's patience with the buyer's injustice is considered good character, and he will be rewarded for it. If the buyer is in hardship, the merchant must grant him a delay, and it is commendable for him to waive all or part of the debt. It is not permissible to count the waived money towards the obligatory Zakat (definition), and the patient, trustworthy merchant will receive a great reward.