It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Do not withhold the milk in the udder of a she-camel or a goat for the purpose of selling it. Whoever buys such an animal, after milking it, has two options: if he is pleased with the sale, he may keep it; if he is displeased, he may return the animal and along with it give one sa’ of dates."
Hadith Referenceالسنن المأثورة / باب في البيوع / 257
Hadith Takhrijسنن نسائی، البيوع، باب النهي عن المصراة، رقم: 4487 وقال الالباني: صحيح، مسند الحمیدی: 446/2، رقم: 1028