Is it permissible for an adoptive parent to bequeath inheritance to his adopted child, and what is the ruling on purchasing from this child after the death of his adoptive father?

Adoption is a pre-Islamic practice that Islam abolished. Allah Almighty says: "Nor has He made your adopted sons your [true] sons" and "Call them by [the names of] their fathers; it is more just in the sight of Allah." Since adoption is forbidden and invalid, inheritance through it is also invalid. Therefore, whoever buys something from an adopted person after the death of their adopter, which the adopted person inherited from them, has sold something they do not own. This sale, which is the sale of another's property without authorization or guardianship ( فضولي - unauthorized person's sale), is a matter of dispute among jurists. The Hanafis, Malikis, and one narration from Ahmad held that it is permissible, and its enforcement depends on the owner's approval, while Al-Shafi'i and Ahmad, in another narration, held that it is void. An exception to this is if all the heirs are adults and of sound mind, and they have permitted the adopted person to inherit with them; in this case, they are considered as if they have gifted him something from their own property.