Sahih Bukhari, Chapter: Sales and Trade

Here (i.e. in Makkah) there was a man called Nawwas and he had camels suffering from the disease of excessive and unquenchable thirst. Ibn Umar went to the partner of Nawwas and bought those camels. The man returned to Nawwas and told him that he had sold those camels. Nawwas asked him, "To whom have you sold them?" He replied, "To such and such Sheikh." Nawwas said, "Woe to you; By Allah, that Sheikh was Ibn Umar." Nawwas then went to Ibn Umar and said to him, "My partner sold you camels suffering from the disease of excessive thirst and he had not known you." Ibn Umar told him to take them back. When Nawwas went to take them, Ibn Umar said to him, "Leave them there as I am happy with the decision of Allah's Apostle that there is no oppression."