Is zakat obligatory on the monthly stipend a student receives from the university, and what must he do regarding past years in which he did not pay zakat?

There is no Zakat on a monthly salary the moment it is received, based on the statement of Ibn Umar, may Allah be pleased with him: "Whoever benefits from money, there is no Zakat on it until a year has passed over it." This is also the view of the Four Imams. If the saved money reaches the nisab (minimum threshold) and a year has passed over it, then Zakat becomes obligatory on it, based on the statement of the Messenger of Allah, peace and blessings be upon him: "There is no Zakat on money until a year has passed over it." As for past years in which a nisab of money was available and a year passed over it, its Zakat must be paid.