Musnad Ahmad 30:580

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Ayyub, from Ibn Sirin, from Abu Hurayrah, that the Prophet (peace and blessings of Allah be upon him) said: "Whoever buys a *musarrah* (an animal whose milk has been withheld in the udder to deceive the buyer) ewe, he shall milk it. If he is pleased with it, he keeps it; and if not, he returns it and returns with it a *sa'* of dates."