Musnad Ahmad 30:3109

Waki' narrated to us, he said: Hammad ibn Salamah narrated to us, from Muhammad ibn Ziyad, from Abu Hurairah, from the Prophet, peace and blessings of Allah be upon him: "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."