Musnad Abu Ya'la al-Mawsili 112:12

Humaid ibn Mas'adah al-Sami narrated to us, 'Ar'arah ibn al-Barand narrated to us, Isma'il al-Makki narrated to us, from al-Hasan, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not practice *talamus* (touching goods to conclude a sale without inspection), do not practice *tanajush* (bidding up the price without the intention to buy), do not trade in *gharar* (uncertainty/risk), and let no city dweller sell on behalf of a bedouin. Whoever buys a *muhaffalah* (an animal whose milk has been withheld in the udder to deceive the buyer), let him milk it for three days. If he returns it, let him return it along with a *sa'* of dates."