(2) باب مَا كَانَ مِنْ خَلِيطَيْنِ فَإِنَّهُمَا يَتَرَاجَعَانِ بَيْنَهُمَا بِالسَّوِيَّةِ فِي الصَّدَقَةِ
Narrated Anas:
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.
Reference: Sahih al-Bukhari 2487
In-book reference: Book 47, Hadith 5
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 44, Hadith 667