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."
قُلْ يَا أَيُّهَا النَّاسُ إِنِّي رَسُولُ اللّهِ إِلَيْكُمْ جَمِيعًا الَّذِي لَهُ مُلْكُ السَّمَاوَاتِ وَالأَرْضِ لا إِلَـهَ إِلاَّ هُوَ يُحْيِـي وَيُمِيتُ فَآمِنُواْ بِاللّهِ وَرَسُولِهِ النَّبِيِّ الأُمِّيِّ الَّذِي يُؤْمِنُ بِاللّهِ وَكَلِمَاتِهِ وَاتَّبِعُوهُ لَعَلَّكُمْ تَهْتَدُونَ (7:158) [Say, O Muhammad]: 'O men! I am Allah's Messenger to you all - of Him to Whom belongs the dominion of the heavens and the earth. There is no god but He. He grants life and deals death. Have faith then, in Allah and in His Messenger, the ummi Prophet who believes in Allah and His words; and follow him so that you may be guided aright.'