Is it permissible for a charitable organization that has undertaken to cover the university tuition fees of a student to stipulate that he allocate a portion of his salary to the needy after his graduation and employment?

What a charitable organization gives to a student could be zakat, sadaqah (charity), waqf (endowment), or a loan. It is not permissible to stipulate that a portion of his future salary be allocated to the needy, because the intent is benevolence, not exchange. It is better that the money be given as outright ownership if he is deserving, and the organization should limit itself to inviting and encouraging benevolence without compulsion.