Musnad Ahmad 26:546

Yahya narrated to us, from al-Taymi, from Abu Uthman, from Ibn Mas’ud: "Whoever buys a *muhaffalah*—and perhaps he said: a *muhaffalah* sheep—let him return it, and return with it a *sa’* [of food]." And the Prophet, may Allah bless him and grant him peace, forbade meeting the caravans for trade.