Musannaf Ibn Abi Shaybah

The Prophet (peace be upon him), may Allah have mercy on him, says that Abdullah bin Umar (may Allah be pleased with them both) bought two camels and left them among the camels of charity. Then both of them became very healthy and large, and their condition became very good. The narrator says: Umar (may Allah be pleased with him) saw those camels and found their condition strange and asked: Whose camels are these? People replied: They belong to Abdullah bin Umar (may Allah be pleased with them both). He (may Allah be pleased with him) said: Sell both of them and take your original amount. And whatever extra amount there is, return it to the treasury (Bayt al-Mal).