the Messenger of Allah said: "I have exempted charity on horses and slaves. So bring charity for silver, one Dirham for every forty Dirham. There is nothing for me (to collect) on one hundred and ninety Dirham, so when it reaches two hundred, then five Dirham of it (are due)."  

قَالَ رَسُولُ اللَّهِ ﷺ قَدْ عَفَوْتُ عَنْ صَدَقَةِ الْخَيْلِ وَالرَّقِيقِ فَهَاتُوا صَدَقَةَ الرِّقَةِ مِنْ كُلِّ أَرْبَعِينَ دِرْهَمًا دِرْهَمًا وَلَيْسَ فِي تِسْعِينَ وَمِائَةٍ شَيْءٌ فَإِذَا بَلَغَتْ مِائَتَيْنِ فَفِيهَا خَمْسَةُ الدَّرَاهِمِ وَفِي الْبَابِ عَنْ أَبِي بَكْرٍ الصِّدِّيقِ وَعَمْرِو بْنِ حَزْمٍ