Is taking an orphan's wealth haram?

Haram Money & business Quran · 2 Hadith · 1

Short answer

Yes. Allah warns that those who consume the wealth of orphans unjustly only consume fire into their bellies (4:10). The Prophet ﷺ counted it among the seven great destructive sins.

Evidence

Quran

إِنَّ ٱلَّذِينَ يَأْكُلُونَ أَمْوَٰلَ ٱلْيَتَٰمَىٰ ظُلْمًا إِنَّمَا يَأْكُلُونَ فِى بُطُونِهِمْ نَارًۭا ۖ وَسَيَصْلَوْنَ سَعِيرًۭا ﴿١٠﴾

Lo! Those who devour the wealth of orphans wrongfully, they do but swallow fire into their bellies, and they will be exposed to burning flame.

وَلَا تَقْرَبُوا۟ مَالَ ٱلْيَتِيمِ إِلَّا بِٱلَّتِى هِىَ أَحْسَنُ حَتَّىٰ يَبْلُغَ أَشُدَّهُۥ ۖ وَأَوْفُوا۟ ٱلْكَيْلَ وَٱلْمِيزَانَ بِٱلْقِسْطِ ۖ لَا نُكَلِّفُ نَفْسًا إِلَّا وُسْعَهَا ۖ وَإِذَا قُلْتُمْ فَٱعْدِلُوا۟ وَلَوْ كَانَ ذَا قُرْبَىٰ ۖ وَبِعَهْدِ ٱللَّهِ أَوْفُوا۟ ۚ ذَٰلِكُمْ وَصَّىٰكُم بِهِۦ لَعَلَّكُمْ تَذَكَّرُونَ ﴿١٥٢﴾

And approach not the wealth of the orphan save with that which is better, till he reach maturity. Give full measure and full weight, in justice. We task not any soul beyond its scope. And if ye give your word, do justice thereunto, even though it be (against) a kinsman; and fulfil the covenant of Allah. This He commandeth you that haply ye may remember.

Hadith

1 Sahih al-Bukhari 2766

Narrated Abu Huraira:The Prophet (ﷺ) said, "Avoid the seven great destructive sins." The people enquired, "O Allah's Messenger (ﷺ)! What are they?" He said, "To join others in worship along with Allah, to practice sorcery, to kill the life which Allah has forbidden except for a just cause, (according to Islamic law), to eat up Riba (usury), to eat up an orphan's wealth, to give back to the enemy and fleeing from the battlefield at the time of fighting, and to accuse, chaste women, who never even think of anything touching chastity and are good believers

Arabic text (with chain of narrators)

حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ عَبْدِ اللَّهِ، قَالَ حَدَّثَنِي سُلَيْمَانُ بْنُ بِلاَلٍ، عَنْ ثَوْرِ بْنِ زَيْدٍ الْمَدَنِيِّ، عَنْ أَبِي الْغَيْثِ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏"‏ اجْتَنِبُوا السَّبْعَ الْمُوبِقَاتِ ‏"‏‏.‏ قَالُوا يَا رَسُولَ اللَّهِ، وَمَا هُنَّ قَالَ ‏"‏ الشِّرْكُ بِاللَّهِ، وَالسِّحْرُ، وَقَتْلُ النَّفْسِ الَّتِي حَرَّمَ اللَّهُ إِلاَّ بِالْحَقِّ، وَأَكْلُ الرِّبَا، وَأَكْلُ مَالِ الْيَتِيمِ، وَالتَّوَلِّي يَوْمَ الزَّحْفِ، وَقَذْفُ الْمُحْصَنَاتِ الْمُؤْمِنَاتِ الْغَافِلاَتِ ‏"‏‏.‏

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This is general information, not a fatwa. For your own situation, ask a qualified scholar.