Sa'id bin Jubayr narrates from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that when this verse was revealed: "And do not approach the property of the orphan except in the best manner." [Surah al-An'am: 152], the people separated the property of the orphans from their own property, and food would spoil and meat would go bad. They complained to the Messenger of Allah (peace and blessings be upon him), and Allah revealed this verse: "Improvement for them is best; and if you mix with them, then they are your brothers." [Surah al-Baqarah: 220] Then they mixed them in with themselves.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10360