Reference for Bava Batra 59:2
קשיא דרבא אדרבא קשיא דרב נחמן אדרב נחמן
There was a piece of land which was called Bar Sisin's, but the vendor said, 'This is not really the property of Bar Sisin though it is called Bar Sisin's.' The case was brought before R. Nahman, and he decided in favour of the purchaser. Said Raba to him: Is this a right decision? Does not the onus probandi always lie on the claimant? There is thus a contradiction between these two remarks of Raba, and also between the two rulings of R. Nahman.<span class="x" onmousemove="('comment',' Because in the former case Raba decides in favour of the purchaser and R. Nahman in favour of the seller, and in the latter case Raba decides in favour of the seller and R. Nahman in favour of the purchaser. ');"><sup>2</sup></span>