Musannaf Ibn Abi Shaybah

Hazrat Tawus says that when the wealth of two persons is mixed together, it will not be combined for (the purpose of) zakat.

Hazrat Ibn Jurayj says that I informed Ata about the statement of Tawus, so he said that I also consider this to be correct.

Imam Zuhri states that when one person has twenty goats and another person also has twenty goats, and both persons have the same shepherd who takes them together and brings them back together, then zakat is obligatory on them. (Zakat is due on the combined total of both.)