What verse in the Quran made adoption haram (forbidden) in Islam?
Quran 33:5
Proclaim their real parentage. That will be more equitable in the sight of Allah.
And if ye 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 ye make unintentionally, but what your hearts purpose (that will be a sin for you).
Allah is ever Forgiving, Merciful.
33:5