Musnad Ahmad 937:273

Abu Abd al-Rahman narrated to us, Sa'id ibn Abi Ayyub narrated to us, Ubayd Allah ibn Abi Ja'far narrated to me, from Salim ibn Abi Salim al-Jayshani, from his father, from Abu Dharr, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "O Abu Dharr, do not take charge of the wealth of an orphan, and do not be a commander over two people."