Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates: In the blessed time of the Prophet Muhammad (peace be upon him), there was a man who used to buy and sell, and he had a stammer in his speech. His family came to the service of the Prophet (peace be upon him). They said: O Messenger of Allah, please stop so-and-so from conducting transactions because he buys and sells, but his speech is not clear. The Prophet (peace be upon him) called him and forbade him from buying and selling. So he said: O Messenger of Allah (peace be upon him), I cannot manage without buying and selling. Then the Prophet (peace be upon him) said: If you do not stop buying and selling, then say: "This is it and this is it, and there will be no deception."