Is there an allowance in Islamic inheritance law for a father to write his will of inheritance in favour of a specific child in return of his special care towards the parent compared to the other children who were able to devote less attention?
Yes, it is allowed for any one to make a will in favor of any one whether a son or wife or friend or any one whom he wants. The will is obligatory in one third of the estate, but if it goes more than one third, then it will require the permission of the inheritors in the part which is more than the one third.
Wassalam.