What is the ruling on purchasing a period of government service to complete the required years of work for a full retirement pension, and is this considered usury?

The permissibility of paying installments for future years to obtain early retirement depends on the permissibility of the retirement contract itself. If the retirement system is cooperative and based on mutual solidarity – as is common in government systems – then there is no harm in subscribing to it and receiving a retirement salary, provided that the state does not oblige the employee to engage in commercial insurance. However, if the system is commercial or obligatory with commercial insurance involved, then any amount exceeding what was paid must be disposed of for charitable causes. Based on this, if the retirement system is originally permissible, then there is no objection to expediting the payment of due amounts before their due date, because it is an expedited payment of an obligated debt.