A Forbidden and Invalid Bequest

Question :

A man fathered two sons and bequeathed a house to be owned by one of them, then he married after the death of his wife and fathered a son. What is his share of the inheritance?

Answer:

To this man who fathered two sons and left a house to be owned by one of them, we say, that this bequest of his is forbidden and invalid. This is because it apportions to one of the heirs something from his wealth, and because it entails partiality towards one of his sons over another, and both of these things are forbidden. As for the first, it is because bequests for heirs are forbidden, since it transgresses the limits set by Allah, the Almighty, the All-Powerful. Because He, Most Glorified, Most High apportioned inheritances in accordance with His Knowl- edge and His Wisdom. He says, in the first Verse dealing with inheritance:
"You know not which of them, whether your parents or your children, are nearest to you in benefit; (these fixed shares) are ordained by Allah. And Allah is Ever All-Knower, All-Wise."

And in the second Verse, He says:
"These are the limits (set by) Allah, and whosoever obeys Allah and His Messenger will be admitted to Gardens under which rivers flow (in Paradise), to abide therein, and that will be the great success. And whosoever disobeys Allah and His Messenger and transgresses His limits, He will cast him into the Fire, to abide therein; and he shall have a disgraceful torment."

and in the third Verse, He says:
"(Thus) does Allah make clear to you (His Law) lest you go astray. And Allah is the All-Knower of everything."

As for the second matter, which is the display of partiality towards one son over another, it is an act of injustice and wrongdoing and it is reported in the Two Sahihs, on the authority of An-Nu'man bin Bashir, may Allah be pleased with him, that his father gave him a gift and his mother (i.e. the mother of An-Nu'man) said: "I will not be happy until you call upon the Prophet ﷺ to witness it." An-Nu'man bin Bashir, may Allah be pleased with him, said: "So my father took me to the Messenger of Allah and said: "O Messenger of Allah! I testify that I have given a gift of such-and-such from my propert to An-Nu'man," and the Prophet said:
"Have you given the same as you gave to An-Nu'man to all of your sons?"

He replied: "No." The Prophet said:
"Then ask someone else to witness it."

He said:
"Would you like them to display equal obedience to you?"

He said: "Yes." He said:
"Then do not do it."

And the Prophet said:
"Fear Allah and act with justice between your children."

From this it is clear that it is not permissible to prefer one child over another, because this is unjust.

As for the questioner mentioning that this man married after the death of his wife, and fathered a son, so what is his share of the inheritance? It is not possible to reply to that, until the inheritance has been defined and it has been ascertained who are the heirs and what he is entitled to from the remainder of the inheritance.