Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever buys a goat whose milk has been held back in its udders has the option for three days. If he wishes he may keep it, and if he wishes he may return it, and give a sa' of dates along with it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10730