Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "Do not hold back the milk of camels and goats. Whoever buys such an animal has two options after milking it: if he is pleased with it he may keep it, and if he is displeased he may return it along with a sa' of dates."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10713