حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عُمَرَ بْنَ الْخَطَّابِ، قَالَ اتَّجِرُوا فِي أَمْوَالِ الْيَتَامَى لاَ تَأْكُلُهَا الزَّكَاةُ ‏.‏

Yahya related to me from Malik that he had heard that Umar ibnal-Khattab said, "Trade with the property of orphans and then it willnot be eaten away by zakat." Translation Not Available

Book Ref: Muwatta Imam Malik Book 17 Hadith 592
Web Ref:  Muwatta Imam Malik Book 17 Hadith 12