Muwatta Malik 591

وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَائِشَةَ، زَوْجَ النَّبِيِّ صلى الله عليه وسلم كَانَتْ تُعْطِي أَمْوَالَ الْيَتَامَى الَّذِينَ فِي حَجْرِهَا مَنْ يَتَّجِرُ لَهُمْ فِيهَا ‏.‏

Yahya related to me from Malik that he had heard that A'isha, the wife of the Prophet, may Allah bless him and grant him peace, used to give the property of the orphans that were in her house to whoever would use it to trade with on their behalf

Reference

Muwatta Malik 591

In-book

Book 17, Hadith 14