What is the ruling on money received by an employee from his work during an intermittent absence that lasted several months, knowing that he submitted a retirement request afterwards and his years of service were calculated as 17 years less?

Fulfilling the terms of a contract is obligatory, based on Allah’s saying: "O you who have believed, fulfill [all] contracts," and the Prophet's (peace be upon him) saying: "Muslims are bound by their conditions." Therefore, it is not permissible to take salary for unauthorized days of absence, and what was taken must be returned to the concerned party.

However, if the questioner has a lost financial right with their employer, such as if their period of service was calculated as less than what they actually worked, then there is no harm in them keeping the salary for the days of absence if its amount is less than or equal to their lost right. This is known as the issue of "al-Zafar" (taking one’s right by force or stratagem).