Giving a gift to one child specifically for his success

Question:
Honorable Shaykh, may Allah grant you success. A questioner says: Is it permissible for a father to give a gift specifically to his son if his son passed the exams and the other one failed?

Answer:
No, it is not permissible. But it is permissible to give specifically if there is a reason, such as one of them being poor, so he gives to him because of his poverty, not to give to him by way of honoring him, but because of his poverty, and there is no harm in that. Or if he has a debt and he pays off the debt for him, there is no harm in that.