Muwatta Imam Malik Book of Zakat, Hadith 29

Yahya related to me from Malik from Yahya ibn Said that Muhammad ibn Yahya ibn Habban said, "Two men from the Ashja tribe told me that Muhammad ibn Maslama al-Ansari used tocome to them to collect their zakat, and he would say to anyone who owned livestock, 'Select (the animal for) the zakat on your livestock and bring it to me,' and he would accept any sheep that was brought to him provided it met the requirements of what the man owed."
Malik said, "The sunna with us, and what I have seen the people of knowledge doing in our city, is that things are not made difficult for the muslims in their paying zakat, and whatever they offer of their livestock is accepted from them."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ مُحَمَّدِ بْنِ يَحْيَى بْنِ حَبَّانَ، أَنَّهُ قَالَ أَخْبَرَنِي رَجُلاَنِ، مِنْ أَشْجَعَ أَنَّ مُحَمَّدَ بْنَ مَسْلَمَةَ الأَنْصَارِيَّ، كَانَ يَأْتِيهِمْ مُصَدِّقًا فَيَقُولُ لِرَبِّ الْمَالِ أَخْرِجْ إِلَىَّ صَدَقَةَ مَالِكَ . فَلاَ يَقُودُ إِلَيْهِ شَاةً فِيهَا وَفَاءٌ مِنْ حَقِّهِ إِلاَّ قَبِلَهَا . قَالَ مَالِكٌ السُّنَّةُ عِنْدَنَا - وَالَّذِي أَدْرَكْتُ عَلَيْهِ أَهْلَ الْعِلْمِ بِبَلَدِنَا - أَنَّهُ لاَ يُضَيَّقُ عَلَى الْمُسْلِمِينَ فِي زَكَاتِهِمْ وَأَنْ يُقْبَلَ مِنْهُمْ مَا دَفَعُوا مِنْ أَمْوَالِهِمْ .