It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever buys an animal whose milk has been held back in its udders has the option for three days. If he returns it, he should give a sa' of grain, other than wheat."
Imam al-Bukhari (may Allah have mercy on him) said: Some narrated from Ibn Sirin: "a sa' of grain, and he has the option for three days."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10731