Sunan an-Nasai Book 30, Hadith 3670

أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا عِمْرَانُ بْنُ عُيَيْنَةَ، قَالَ حَدَّثَنَا عَطَاءُ بْنُ السَّائِبِ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ، فِي قَوْلِهِ ‏{‏إِنَّ الَّذِينَ يَأْكُلُونَ أَمْوَالَ الْيَتَامَى ظُلْمًا‏}‏ قَالَ كَانَ يَكُونُ فِي حِجْرِ الرَّجُلِ الْيَتِيمَ فَيَعْزِلُ لَهُ طَعَامَهُ وَشَرَابَهُ وَآنِيَتَهُ فَشَقَّ ذَلِكَ عَلَى الْمُسْلِمِينَ فَأَنْزَلَ اللَّهُ عَزَّ وَجَلَّ ‏{‏وَإِنْ تُخَالِطُوهُمْ فَإِخْوَانُكُمْ‏}‏ ‏{‏فِي الدِّينِ‏}‏ فَأَحَلَّ لَهُمْ خُلْطَتَهُمْ‏.‏

It was narrated that Ibn 'Abbas said -concerning the Verse:"Verily, those who unjustly eat up the property of orphans" -A man would have an orphan in his care, and he would keep his food, drink and vessels separate. This caused hardship to the Muslims, so Allah, the Mighty and Sublime, revealed: "And they ask you concerning orphans. Say: The best thing is to work honestly in their property, and if you mix your affairs with theirs, then they are your brothers" (in religion), so it is permissible for you to mix with them