Short answer
Caring for a child as your own is allowed and greatly rewarded. What Islam forbids is changing the child's lineage: claiming the child as your biological son or daughter. Many Western adoption orders do exactly that, so Hanafi muftis advise guardianship or kafalah instead, and permit an order only under strict conditions when there is no other way.
Tabanni (adoption that transfers lineage) has no effect in the Shariah and claiming such lineage is haram. Kafalah, raising and providing for a child who keeps their own lineage, is a virtue. An adoptive child is not an heir and is not a mahram through adoption alone.
The four schools agree on this.
Explanation
Before Islam, an adopted son took his adoptive father's name and inherited as a son. Zayd ibn Harithah was known as Zayd ibn Muhammad until the Quran said that adopted sons are not your true sons and told the believers to call them by their fathers' names. The Prophet ﷺ warned that whoever knowingly claims a father other than his own is barred from Paradise. The four schools agree on this.
What is allowed: taking in a child, loving them, providing for them, and raising them as part of your family. This is kafalah (sponsorship), and the reward for it is among the greatest in Islam. See the reward for caring for an orphan.
The problem with some adoption orders. In the UK, the US and many other countries, a full adoption order ends the birth parents' legal status and issues a new birth certificate naming the adoptive parents as the parents. The child inherits as a natural child. These effects clash with the rules of lineage, inheritance and mahram.
Better routes: special guardianship in the UK, legal guardianship in the US, long-term fostering, or kafalah where the law recognises it. These give security without rewriting lineage.
If an adoption order is the only way to give a child a home, many muftis permit it with conditions:
- Keep the child's real lineage known to them and recorded. See telling a child they are adopted.
- Do not present the child as your biological child in religious matters, such as nikah.
- Observe hijab rules as the child nears puberty, unless a milk tie exists.
- Write an Islamic will: an adopted child does not inherit as an heir, but you may leave them up to one third by bequest.
Ask a mufti about your own case. This answer explains the general ruling. When the details of your situation matter, as they do here, ask a qualified mufti and give them the full facts. Where to ask a scholar.
The evidence
Quran, Surah Al-Ahzaab 33:4
مَّا جَعَلَ ٱللَّهُ لِرَجُلٍۢ مِّن قَلْبَيْنِ فِى جَوْفِهِۦ ۚ وَمَا جَعَلَ أَزْوَٰجَكُمُ ٱلَّٰٓـِٔى تُظَٰهِرُونَ مِنْهُنَّ أُمَّهَٰتِكُمْ ۚ وَمَا جَعَلَ أَدْعِيَآءَكُمْ أَبْنَآءَكُمْ ۚ ذَٰلِكُمْ قَوْلُكُم بِأَفْوَٰهِكُمْ ۖ وَٱللَّهُ يَقُولُ ٱلْحَقَّ وَهُوَ يَهْدِى ٱلسَّبِيلَ ﴿٤﴾
Allah has not made for a man two hearts in his interior. And He has not made your wives whom you declare unlawful your mothers. And he has not made your adopted sons your [true] sons. That is [merely] your saying by your mouths, but Allah says the truth, and He guides to the [right] way.
Adoption does not create real lineage.
Quran, Surah Al-Ahzaab 33:5
ٱدْعُوهُمْ لِءَابَآئِهِمْ هُوَ أَقْسَطُ عِندَ ٱللَّهِ ۚ فَإِن لَّمْ تَعْلَمُوٓا۟ ءَابَآءَهُمْ فَإِخْوَٰنُكُمْ فِى ٱلدِّينِ وَمَوَٰلِيكُمْ ۚ وَلَيْسَ عَلَيْكُمْ جُنَاحٌۭ فِيمَآ أَخْطَأْتُم بِهِۦ وَلَٰكِن مَّا تَعَمَّدَتْ قُلُوبُكُمْ ۚ وَكَانَ ٱللَّهُ غَفُورًۭا رَّحِيمًا ﴿٥﴾
Call them by [the names of] their fathers; it is more just in the sight of Allah. But if you do not know their fathers - then they are [still] your brothers in religion and those entrusted to you. And there is no blame upon you for that in which you have erred but [only for] what your hearts intended. And ever is Allah Forgiving and Merciful.
The child keeps their own lineage.
Sahih al-Bukhari 6766
Sahih... من ادعى إلى غير أبيه وهو يعلم أنه غير أبيه فالجنة عليه حرام ...
"Whoever claims a father other than his own, knowing he is not his father, Paradise is forbidden to him."
Changing lineage is a grave sin.
Where the ruling is recorded
- al-Hidaya, Kitab al-Laqit (the foundling). Caring for an abandoned child is a virtue; lineage is not established by claim alone without its conditions.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Wasaya. A bequest to a non-heir is valid up to one third.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.