Muwatta Imam Malik (Riwayat Ibn al-Qasim)

And with the same chain of narration (it is narrated from Sayyiduna Ibn Umar, may Allah be pleased with them both) that a man was mentioned before the Messenger of Allah, peace and blessings be upon him, who used to be deceived in buying and selling. So the Messenger of Allah, peace and blessings be upon him, said to him: "When you sell something, say: 'There is no deception.'" Then, whenever that man sold something, he would say: "There is no deception."