The ruling in Sharia on those who differentiate between children when giving gifts and prefer some over others
In answer to this, we say that it is haram. The Messenger of Allah ﷺ forbade it, and he said to Bashir ibn Sa’d al-Ansari, who had preferred his son Nu’man in giving a gift: “Fear Allah and be just among your children.”
Also, the Prophet ﷺ said: “I do not act as a witness to injustice.”
He ﷺ refused to be a witness to it and said: “Take someone other than me as a witness to this.”
Therefore, it is not permissible for anyone to show partiality towards some of his children, rather he should distribute gifts equally among them, just as Allah the Exalted has maintained equality among them, giving a male the share equal to two females. This concerns only giving gifts and giving out of goodwill. But whatever a father gives to his children because of their need, the justice in it is that he gives each one according to his need, whether what he has given to others is more or less than that.
For example, if the eldest son needs books and stationery, he should give him an amount with which he can buy his books and other necessities for the madrasa, and giving the others, who do not have such a need, an equal amount is not required; there is no preference for the eldest son in this, rather it is justice. When the others also reach the stage of the eldest and they too need the items the eldest needed, then he should give them as much as he gave the eldest.
There is another issue here: some people, when their eldest child becomes of marriageable age, arrange his marriage during their lifetime. Then they bequeath to the younger children, whose marriage has not yet taken place, an amount of wealth equal to what was spent on the marriage of the elder ones. This is haram, and it is not permissible to act upon this bequest that he made for them. It should be returned to the estate, and the inheritance should be distributed among the heirs according to the Sharia method.