What is the ruling on money earned from selling lecture notes to students, given that purchase is obligatory, the price is high, students sometimes benefit little from them, and taking into consideration that faculty members' salaries are low? And does the ruling differ if they are sold at cost or with a small profit?

There is no objection to faculty members selling beneficial notes to students at a price agreed upon by both parties. It is not necessary for the price to be the cost price or a small profit, as long as the sale is based on mutual consent; as Allah Almighty says: "O you who have believed, do not consume one another's wealth unjustly but only [in lawful] business by mutual consent." It is not considered coercion for the university to require students to take courses that necessitate buying specific notes, because by entering the university, the student has committed to its rules and regulations, and thus, consent to purchase these notes is initially obtained from them.