How does a man divide and purify the inheritance of his deceased mother, knowing that he used to manage the family's financial affairs from his salary and his mother's money, which he collected from her real estate business with her authorization, and that he did not differentiate between his money and hers?

If the son is unable to distinguish his mother's money from his own, he must strive and exercise caution to identify his mother's money, and it should be divided among her heirs, just as if his money became mixed with unlawful money and he could not ascertain its amount.

If the matter becomes unclear to him and he does not know how much is unlawful and how much is lawful, he should endeavor to determine the amount of the unlawful money and return it to its rightful owners, or give it in charity on their behalf if he despairs of finding them.

As for zakat, if the mixed money reaches the nisab and a year has passed over it without its zakat being paid, then its zakat is due before its distribution. This is based on the principle of the absolute effect of commingling, which is the view of the Shafi'is.