(Mishnah): Any chazakah that does not have with it a claim, is not a chazakah.

How is this? If the owner asked him, "Why are you in my property?" and he replied, "Because no-one said anything to me", that is not a chazakah.

But if he replied, "You sold it to me" or "you gave it to me as a gift", it is a chazakah.

If he inherited the field, he does not need to know and claim how his father received it.

(Gemara): Although an inheritor does not need to claim, he does need a chazakah (of 3 years on the land).

Mishnah in Maseches Kesuvos: R. Yehoshua admits (since it is a monetary case rather than 'issur') that if Reuven said to Shimon, "This field used to belong to your father and I bought it from him", (that he is believed. The Gemara there explains that since without Reuven's first statement, Shimon would have had no ability to claim that the field was his, we also believe Reuven's second statement. However, if Shimon had witnesses that it had originally belonged to his father, Reuven is not believed. This is only true if Reuven did not have three years of chazakah on the field, otherwise, he is believed.)

Gemara in Kesuvos: If Reuven is in possession of a field and consuming its produce and Shimon brings witnesses that his father had died with it in his possession, we take it away from Reuven and award it to Shimon (since Reuven had not claimed that he had bought it from Shimon's father).

The question is - what is the law if Reuven went and brought witnesses that Shimon's father had not died with it in his possession?

Rav Nachman bar Yaakov: I was the one who originally ruled that the land must be taken away from Reuven and I then ruled that it must be returned to him. (It became a case of two against two witnesses and we therefore revert back to the original situation, that Reuven was possession.)

Rav: When you took the field away from Reuven, it was done according to the ruling of Beis Din; after this, the burden of proof is upon the one who wishes to extract it from the other.

Question: Which person must therefore bring proof?

R. Ba: The witnesses to the father's death testify for Shimon that he owned it when he died. There are no other witnesses who could be used.

R. Yosi: The field reverts back to its original owner and the new resident must bring proof in order to take it.