"The Messenger of Allah said: 'Dates for dates, wheat for wheat, barley for barley, salt for salt, exchanged hand to hand. Whoever gives more or takes more has engaged in Riba unless they are of different types."  

قَالَ رَسُولُ اللَّهِ ﷺ التَّمْرُ بِالتَّمْرِ وَالْحِنْطَةُ بِالْحِنْطَةِ وَالشَّعِيرُ بِالشَّعِيرِ وَالْمِلْحُ بِالْمِلْحِ يَدًا بِيَدٍ فَمَنْ زَادَ أَوِ ازْدَادَ فَقَدْ أَرْبَى إِلاَّ مَا اخْتَلَفَتْ أَلْوَانُهُ