Baba Metzia 1:2-3

Baba Metzia 1:2

If two people were riding on an animal, or one was riding on the animal and the other was leading it, and each of them claims exclusive ownership, each one swears that no less than half belongs to him and it is divided between them. Whenever the parties admit that they found an object simultaneously, or if there are witnesses to that effect, they divide the item without taking an oath.

Baba Metzia 1:3

If a person is riding on an animal and he sees a lost object, so he tells another person to hand it to him but the other person picks it up and says he has acquired it for himself, that second person gets to keep it. If he hands it to the first person and then says that he acquired it for himself, his words are of no consequence.