Adoption is forbidden in Islam is most certain. In verses 4 and 5 of Surah 33, entitled “Al-Ahzab” or “The Clans” we read what may be rendered in translation as follows: “nor has He made your wives whom you declare (to be your mothers) your mothers, nor has He made those whom you claim (to be your sons) your sons. This is but a saying of your mouths. But Allah says the truth and He shows the way. Proclaim their real parentage. That will be more equitable in the sight of Allah. And if you know not their fathers, then they are your brethren in the faith, and your clients. And there is no sin for you in the mistakes that you make unintentionally, but what your hearts purpose (that will be a sin for you). Allah is Forgiving, Merciful”. (33: 4-5)
This is a clear statement of prohibition. When Almighty Allah says that He has not made a particular relationship in a certain fashion, He means that He disapproves of that fashion. When Almighty Allah disapproves something, He forbids it.
This is not to say that a Muslim family may not raise an orphan child or that a woman may not bring up her sister’s children or a man may not look after his brother’s infants. Indeed, such an action is highly rewarded by Almighty Allah. What is more important is to keep the relationship clear and according to the fact. The children must be called after their own parents.
We have also the Holy Prophet’s (sallal laahu alaihi wasallam) Sunnah to confirm this prohibition. The Holy Prophet (sallal laahu alaihi wasallam) had adopted Sayyiduna Zaid Bin Haritha (radi Allahu anhu) as his son before the advent of Islam. Sayyiduna Zaid (radi Allahu anhu) was known from that moment as “Zaid Bin Muhammad”. However when this Quraanic verse was revealed, Zaid (radi Allahu anhu) was called after his own father, Haritha. The Holy Prophet (sallal laahu alaihi wasallam) continued to love Sayyiduna Zaid (radi Allahu anhu) and his children, especially Sayyiduna Usamah (radi Allahu anhu), very dearly.
The question of leaving one’s property by Will to one’s adopted child is truly a separate matter. Islam established a system of inheritance, which is very detailed and fair to all. This system is an essential part of the overall Islamic economic system that ensures the division of property generation after generation. It takes into account the fact that according to Islam, a person is “put in charge” of his property, which belongs to Almighty Allah. Therefore, it is Almighty Allah Who decides how property is divided after death.
If someone raises an orphan child, he can leave a portion of his property by Will. Every person is allowed to bequeath by Will up to one-third of his property, but the beneficiaries of his Will cannot include any of his heirs.