Sahih Muslim Book 010, Hadith Number 3636.
Chapter : Command pertaining to the selling of animal whose udder is tied up.
Abu Huraira (Allah be pleased with him) reported Allah's Apostle (may peace be upon him) as saying: lie who buys a goat having its udder tied up has the option to return it within three days. If he returns it he should pay a sa' of dates. Wheat is not essential.