Is it permissible for me to keep the surplus amount, ranging between one thousand or two thousand, resulting from the difference between the pre-agreed sum of twenty thousand and the actual university expenses, which might be eighteen thousand or twenty thousand? And is this considered ill-gotten wealth?

"Adopting piety (wara'), avoiding doubtful matters (shubuhat), and exercising caution regarding what is lawful (halal (definition)) and unlawful (haram (definition)) is a sound approach, as the Prophet, peace and blessings be upon him, said: 'Whoever guards himself against doubtful matters protects his religion and his honor,' and 'Leave what makes you doubt for what does not make you doubt.'

If a parent provides a sum of money for studies and some of it remains, the parent must be informed. If the parent requests it back, it must be returned. If the parent pardons it, then it becomes lawful for you, because this is a conditional gift, and the condition of the giver must be observed.

If the parent gifts this extra money to you and you have siblings, your siblings must be given an equivalent amount of this extra money, because it is forbidden to favor one child over others unless there is a legitimate Sharia (definition)-compliant reason."