Mishnah for Nazir 72:4

If there were two baskets, one of terumah and one of hullin, and a seah of terumah fell into one of them, but it is not known into which, behold I can assume that it had fallen into that of the terumah. [Two baskets] and it is not known which was of terumah and which of hullin, and he eats from one of them, he is exempt, and the second basket is treated as terumah and subject to the laws of hallah, the words of Rabbi Meir. But Rabbi Yose exempts it. If another person eats from the second basket he is exempt. If one man ate of both, he must repay the value of the smaller of the two.