The obligation of Zakat

'Ibn Abbas(RAH) narrated that:
the Prophet send Muadh to Yemen, and said: “You are going to some people among the People of the Book. Call them to bear witness that none has the right to be worshipped but Allah, and that I am the messenger of Allah. If they obey that, then tell them that Allah has enjoined upon them five prayers every day and night. If they obey that, then tell them that Allah has enjoined upon them charity (Zakat) from their wealth, to be taken from the rich and given to their poor. If they obey that, then beware of (taking) the best of their wealth. And beware of the supplication of the oppressed, for there is no barrier between and Allah.”

حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا وَكِيعُ بْنُ الْجَرَّاحِ، حَدَّثَنَا زَكَرِيَّا بْنُ إِسْحَاقَ الْمَكِّيُّ، عَنْ يَحْيَى بْنِ عَبْدِ اللَّهِ بْنِ صَيْفِيٍّ، عَنْ أَبِي مَعْبَدٍ، مَوْلَى ابْنِ عَبَّاسٍ عَنِ ابْنِ عَبَّاسٍ، أَنَّ النَّبِيَّ ﷺ بَعَثَ مُعَاذًا إِلَى الْيَمَنِ فَقَالَ " إِنَّكَ تَأْتِي قَوْمًا أَهْلَ كِتَابٍ فَادْعُهُمْ إِلَى شَهَادَةِ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَأَنِّي رَسُولُ اللَّهِ فَإِنْ هُمْ أَطَاعُوا لِذَلِكَ فَأَعْلِمْهُمْ أَنَّ اللَّهَ افْتَرَضَ عَلَيْهِمْ خَمْسَ صَلَوَاتٍ فِي كُلِّ يَوْمٍ وَلَيْلَةٍ فَإِنْ هُمْ أَطَاعُوا لِذَلِكَ فَأَعْلِمْهُمْ أَنَّ اللَّهَ افْتَرَضَ عَلَيْهِمْ صَدَقَةً فِي أَمْوَالِهِمْ تُؤْخَذُ مِنْ أَغْنِيَائِهِمْ فَتُرَدُّ فِي فُقَرَائِهِمْ فَإِنْ هُمْ أَطَاعُوا لِذَلِكَ فَإِيَّاكَ وَكَرَائِمَ أَمْوَالِهِمْ وَاتَّقِ دَعْوَةَ الْمَظْلُومِ فَإِنَّهَا لَيْسَ بَيْنَهَا وَبَيْنَ اللَّهِ حِجَابٌ " .