Sahih Bukhari
Obligatory Charity Tax (Zakat)
Volume: 002 / Book Number: 024 / Hadith Number: 530
Narrated Anas:
Abu Bakr wrote to me what was made compulsory by Allah's Apostle 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. (1)