Short answer
Very great. The Prophet ﷺ said that he and the one who looks after an orphan will be in Paradise like two fingers held together. The Quran repeatedly commands kindness to orphans and warns against wronging them or taking their wealth. The four schools agree that caring for an orphan is among the best deeds.
Caring for an orphan, whether a relative or not, is a highly rewarded act of virtue. Maintaining an orphan who has no wealth may become wajib on close relatives under the rules of maintenance, and wronging an orphan or consuming his property is a major sin.
The four schools agree on this.
Explanation
The Prophet ﷺ was himself an orphan: his father died before he was born and his mother when he was six. Allah reminds him of this and commands: as for the orphan, do not oppress him. The four schools agree on what follows from the Quran and sunnah.
What the evidence promises:
- Closeness to the Prophet ﷺ in Paradise: he joined his index and middle fingers and said the guardian of an orphan will be with him like this. Muslim's narration adds that this is so whether the orphan is a relative or a stranger.
- A mark of true faith: the Quran describes the one who pushes the orphan away as the one who denies the religion.
- Feeding the orphan is among the deeds of the righteous, done for Allah's sake alone.
The warning: those who consume the property of orphans unjustly fill their bellies with fire. A guardian must manage an orphan's money honestly and hand it over at maturity. A guardian who is well off should take nothing for this work, and one who is poor may take only a fair amount, as the Quran says.
Ways to earn it today: take an orphaned relative into your home, foster or sponsor a child, or support a well-run orphan programme. On who counts as an orphan see who is an orphan in Islam, and on charity sponsorship see sponsoring an orphan. Taking a child in does not change their name or lineage; see adoption in Islam.
The evidence
Quran, Surah Ad-Dhuhaa 93:9
فَأَمَّا ٱلْيَتِيمَ فَلَا تَقْهَرْ ﴿٩﴾
So as for the orphan, do not oppress [him].
A direct command to treat orphans well.
Quran, Surah Al-Maa'un 107:2
فَذَٰلِكَ ٱلَّذِى يَدُعُّ ٱلْيَتِيمَ ﴿٢﴾
For that is the one who drives away the orphan
Harshness to orphans is described as a trait of those who deny the religion.
Quran, Surah An-Nisaa 4:10
إِنَّ ٱلَّذِينَ يَأْكُلُونَ أَمْوَٰلَ ٱلْيَتَٰمَىٰ ظُلْمًا إِنَّمَا يَأْكُلُونَ فِى بُطُونِهِمْ نَارًۭا ۖ وَسَيَصْلَوْنَ سَعِيرًۭا ﴿١٠﴾
Indeed, those who devour the property of orphans unjustly are only consuming into their bellies fire. And they will be burned in a Blaze.
The warning against wronging orphans in their wealth.
Sahih al-Bukhari 5304
Sahih... أنا وكافل اليتيم في الجنة هكذا ...
"I and the one who looks after an orphan will be in Paradise like this, and he pointed with his index and middle fingers."
The main promise of reward for caring for an orphan.
Sahih Muslim 2983
Sahih... كافل اليتيم له أو لغيره أنا وهو كهاتين في الجنة ...
"The guardian of an orphan, whether a relative of his or not, he and I will be like these two in Paradise."
The reward covers orphans who are not relatives too.
Where the ruling is recorded
- al-Hidaya, Kitab al-Talaq, chapter on maintenance (nafaqa). Maintenance of a poor child falls on relatives when the father has died.
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.