Sahih al-Bukhari 1451
Sahih al-Bukhari · Book 24: Obligatory Charity Tax (Zakat) · If a property is equally owned by two partners, its Zakat is to be paid as a whole
Narrated Anas:
حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ ، قَالَ حَدَّثَنِي أَبِي قَالَ، حَدَّثَنِي ثُمَامَةُ ، أَنَّ أَنَسًا ، حَدَّثَهُ أَنَّ أَبَا بَكْرٍ ـ رضى الله عنه ـ كَتَبَ لَهُ الَّتِي فَرَضَ رَسُولُ اللَّهِ صلى الله عليه وسلم " وَمَا كَانَ مِنْ خَلِيطَيْنِ فَإِنَّهُمَا يَتَرَاجَعَانِ بَيْنَهُمَا بِالسَّوِيَّةِ " .
Abu Bakr wrote to me what Allah's Messenger (ﷺ) has made compulsory (regarding Zakat) and this was mentioned in it: If a property is equally owned by two partners, they should pay the combined Zakat and it will be considered that both of them have paid their Zakat equally.