What is the ruling on the validity of zakat al-fitr exchanged between two families?

Allah has enjoined zakat as a purification for the giver from miserliness, and as a right for the poor. Therefore, it is not permissible for the giver to stipulate a benefit in exchange for giving it, such as stipulating to a debtor that the zakat be returned as payment for a debt. This is because zakat is a right belonging to Allah and to the entitled recipient, and it is not a means for collecting debts. Furthermore, such a condition indicates the miserliness of the giver.