Abu Siba' (may Allah have mercy on him) said: I bought a she-camel from the house of Wathilah bin al-Asqa' (may Allah be pleased with him). When I came out of the house, we found Wathilah bin al-Asqa' (may Allah be pleased with him) dragging his cloak. He said: O servant of Allah! Have you bought the she-camel? I said: Yes. Wathilah (may Allah be pleased with him) said: Has its defect been made clear to you? I said: What is wrong with it? It is outwardly fat and healthy. Wathilah (may Allah be pleased with him) said: Did you buy it for meat, or do you want to ride it? The narrator said: I said: I want to travel on it for Hajj. Wathilah (may Allah be pleased with him) said: There is a hole (a worn spot) in its hoof. Its owner (that is, the one who had owned the she-camel) said: May Allah set you right! You have spoiled the whole deal. Wathilah (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Whoever sells something should state its defect, and it is not lawful for one who knows (the defect) not to make it clear."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10735