Nafi' (may Allah have mercy on him) said that Sayyiduna Ibn Umar (may Allah be pleased with them both) had an orphan's wealth in his care; he would pay its zakah, give it out in mudarabah (a profit-sharing partnership), and borrow from it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشفعة / 11608