Sayyidna Jareer ibn Abdullah, Radi-Allahu anhu, once sent his servant for buying a horse. The servant made a deal for three hundred dirhams and brought the seller with him so he could be paid. Sayyidna Jareer ibn Abdullah, Radi-Allahu anhu, looked at the horse and realized that the seller had undervalued it. "Would you sell it for four hundred?" he asked. The seller agreed. "How about five hundred?" he continued his unusual "bargaining" and finally bought the horse for eight hundred dirhams. He was later asked why he did so. "The seller was not aware of the true value of this horse, " he explained. "I have simply given him a fair price because I had promised to Prophet Muhammad, Sall-Allahu alayhi wa sallam, to always be sincere and well-wisher for every Muslim."
(2:83) Remember that We made a solemn covenant with the children of Israel to this effect: worship none save Allah: be good to your parents, to your relatives, to the orphans and to the helpless; speak aright with the people: establish the Salat and pay the Zakat. But with the exception of a few, you all slid back from it and are paying no heed to it even now.