Is the claim of Ubaid for taking Zayd's flock of sheep by pre-emption valid, knowing that their two flocks were mixed without partnership, and each flock was of a precisely known number and well-defined characteristics?

The reason for preemption (shufa'a) is co-ownership of property or a right thereof. Slaves do not have the right to claim preemption in this herd because he is not a partner to Zayd, and because preemption is established for real estate, not movable property. It is stated in "Matalib Uli an-Nuha": "Preemption is not obligatory for animals, jewels, swords, ships, crops, fruits, or any movable property, because a condition for its obligation is that the sold item be land, as land remains permanently and its harm persists."