that Abu Bakr As-Siddiq wrote to him the law of Zakat which was made obligatory by Allah's Apostle. He wrote: 'Partners possessing joint property (sheep) have to pay its Zakat equally.
أَنَّ أَبَا بَكْرٍ ؓ كَتَبَ لَهُ فَرِيضَةَ الصَّدَقَةِ الَّتِي فَرَضَ رَسُولُ اللَّهِ ﷺ قَالَ وَمَا كَانَ مِنْ خَلِيطَيْنِ فَإِنَّهُمَا يَتَرَاجَعَانِ بَيْنَهُمَا بِالسَّوِيَّةِ
Abu Bakr wrote to me what Messenger of Allah 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.
أَنَّ أَبَا بَكْرٍ ؓ كَتَبَ لَهُ الَّتِي فَرَضَ رَسُولُ اللَّهِ ﷺ وَمَا كَانَ مِنْ خَلِيطَيْنِ فَإِنَّهُمَا يَتَرَاجَعَانِ بَيْنَهُمَا بِالسَّوِيَّةِ