“Abu Ja‘far (a.s.), has said that ’Amir al-Mu’minin, Ali (a.s.), in the case of a man who was ordered by certain persons to ask to sell to them a camel and they had agreed to pay more if it was on credit with deferred payment, and he asked to sell to them a camel and certain ones of them were with him, judged to bar him from charging them more over the cash price with deferred payment.’”