Bequest of wealth to his two sons and to a non-heir, and the hadith: “There is no bequest for an heir”

The questioner:
He says: Honorable Shaykh, may Allah grant you success. I am confused by the statement of the author (may Allah have mercy on him): “And if he bequeaths his wealth to his two sons.” How is a bequest to a son permissible, when the hadith states:

The Shaykh:
He bequeathed all of his wealth, all of his wealth to his two sons and to a non-heir. The bequest here does not exceed one-third, so the wealth is shared between the heirs and the beneficiary of the bequest. The beneficiary of the bequest does not take more than one-third, so there is no harm in this.

The questioner:
Yes.

The Shaykh:
Honorable Shaykh, may Allah grant you success. Also, if he bequeaths to all the heirs, there is no harm in this, because there is no injustice in this. If he bequeaths to all his heirs without singling out any one of them, there is no injustice in this. Yes.