what is the ruling for a student that refuses to share a difficult subject he knows and unable his fellow student to copy his assignment

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The ruling on the non-cooperation of this student with his fellow students in copying his assignments and sharing his knowledge of the subject differs according to the accompanying circumstances. If helping his colleagues in this regard entails cheating and violating the school regulations or laziness and neglect on part of the other students in taking notes or doing their assignments on time, then this student did well by refusing to share with them because cheating is a reprehensible sin. It incurs grave evils on the individual, community and the nation as a whole. The Prophet, sallallaahu ‘alayhi wa sallam, forbade cheating in all matters. He, sallallaahu ‘alayhi wa sallam, said: "He who cheats us is not one of us." [Muslim] Another version of the Hadeeth also cited by Imaam Muslim reads: "He who cheats is not of me."

If students cheated on their assignments or exams, then what would be the point of doing them? Cheating makes the lazy unqualified student pass at the expense of the diligent qualified student. Indeed, this is plain injustice and it goes against the common good. The same applies if those students are too lazy and neglectful to take notes during class and then ask the diligent student to share his notes for them to copy them. He should not help them and share his notes with them so that they would exert greater effort in taking their own notes during class and pay greater attention to their studies.

On the other hand, if sharing those assignments (and notes) with those students does not involve any cheating and it means merely helping them study this difficult subject and benefit from his better understanding of it, then he is advised to help his classmates. In fact, Islam strongly encourages the Muslim to help those in need of his help.

Allaah Knows best.