كتاب البيوع : Hadeeth No:2050 : Abdur-Rahman bin Abu Bakra: that his father said, "The Prophet forbade the selling of gold for gold and silver for silver except if they are equivalent in weight, and allowed us to sell gold for silver and vice versa as we wished."...

كتاب الرقاق : Hadeeth No:6070 : Abu Huraira: The Prophet; said, "A slave (of Allah) may utter a word which pleases Allah without giving it much importance, and because of that Allah will raise him to degrees (of reward): a slave (of Allah) may utter a word (carelessly) which displeases Allah without thinking of its ...