Sahih al-Bukhari 1401
In-book no 1401حَدَّثَنَا 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.