Anas bin Malik reported,

When Abu Bakr appointed him, he wrote for him, "In the name of Allah, the Most Gracious, the Most Merciful. This is the obligatory charity which the Messenger of Allah ﷺ imposed upon the Muslims, which Allah commanded His Messenger to enact." He then mentioned the hadith, in which he said, "What is separate is not to be combined, nor is what is combined to be separated, out of fear of paying charity. Whatever belongs to two partners, they settle accounts between themselves equally."

Azami 3959

Sahih

عن أنس بن مالك قال

إن أبا بكر لما استخلفه كتب له: بسم الله الرحمن الرحيم، هذه فريضة الصدقة التي فرضها رسول الله ﷺ على المسلمين التي أمر الله بها رسوله فذكر الحديث. وقال فيه: لا يجمع بين متفرق ولا يفرق بين مجتمع خشية الصدقة، وما من خليطين فهما يتراجعان بينهما بالسوية.

الأعظمي 3959صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Zakat
Chapter
Zakat on livestock
Section
Prohibition of combining separated flocks or separating combined ones among grazing livestock out of fear of zakat
Numbering
Jami al-Kamil 3959 (2nd edition)
Azami 3959