It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that in the time of the Messenger of Allah (peace and blessings be upon him) there was a man who used to buy and sell, and there was a weakness in his understanding (he lacked sound judgement). His family came to the Prophet (peace and blessings be upon him) and said: O Prophet of Allah, place a restriction on so-and-so, for he trades and there is a weakness in his understanding. The Messenger of Allah (peace and blessings be upon him) summoned him and forbade him (from trading). He said: O Messenger of Allah (peace and blessings be upon him), I cannot bear to give up buying and selling. So he (peace and blessings be upon him) said: "If you cannot give it up, then when you make a deal say: Hand to hand, and there is to be no deception in it."
It seems that when the Prophet (peace and blessings be upon him) saw him, he did not consider him fit to be placed under restriction; and in his not objecting to restriction (hajr) there is evidence that restriction is permissible.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحجر / 11338