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 has the option for three days: if he wishes, he may return it and give a sa' of grain, other than wheat."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10721