The individual property of different people should neither be gathered together nor the joint property should be divided, in assessing the Zakat
حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ الأَنْصَارِيُّ، قَالَ حَدَّثَنِي أَبِي قَالَ، حَدَّثَنِي ثُمَامَةُ، أَنَّ أَنَسًا ـ رضى الله عنه ـ حَدَّثَهُ أَنَّ أَبَا بَكْرٍ ـ رضى الله عنه ـ كَتَبَ لَهُ الَّتِي فَرَضَ رَسُولُ اللَّهِ صلى الله عليه وسلم " وَلاَ يُجْمَعُ بَيْنَ مُتَفَرِّقٍ، وَلاَ يُفَرَّقُ بَيْنَ مُجْتَمِعٍ، خَشْيَةَ الصَّدَقَةِ ".
Narrated Anas: Abu Bakr wrote to me what was made compulsory by Allah's Messenger (ﷺ) and that was (regarding the payments of Zakat): Neither the property of different people may be taken together nor the joint property may be split for fear of (paying more, or receiving less) Zakat.