Al-Sha'bi (may Allah have mercy on him) narrated: Sayyiduna Utbah bin Farqad (may Allah be pleased with him) bought a piece of land on the bank of the Euphrates and used it for growing reeds. When he came to Sayyiduna Umar (may Allah be pleased with him) and mentioned that he had bought a piece of land, he asked: "From whom?" He said: From its owners. When evening came, his companions gathered, and Sayyiduna Umar (may Allah be pleased with him) called him and asked: From whom did you buy the land? He said: From its owners. Sayyiduna Umar (may Allah be pleased with him) asked: "Did you sell him anything?" They said: No. Sayyiduna Umar (may Allah be pleased with him) said: "Then these are its real owners. Return the land to the one from whom you bought it, and take back the price."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14396