Musnad Ahmad 30:1885

Affan narrated to us, Hammad narrated to us, from Muhammad ibn Ziyad, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), who said: "Whoever buys a *musarrah* (an animal whose milk has been withheld in the udder to deceive the buyer) ewe, he has the choice. If he wishes, he may return it along with a *sa'* of dates."