Midrash for Shabbat 21:1
נוֹטֵל אָדָם אֶת בְּנוֹ וְהָאֶבֶן בְּיָדוֹ, וְכַלְכַּלָּה וְהָאֶבֶן בְּתוֹכָהּ. וּמְטַלְטְלִין תְּרוּמָה טְמֵאָה עִם הַטְּהוֹרָה וְעִם הַחֻלִּין. רַבִּי יְהוּדָה אוֹמֵר, אַף מַעֲלִין אֶת הַמְדֻמָּע בְּאֶחָד וּמֵאָה:
A man may carry his son [in a courtyard] with a stone in his (the son's) hand [and we do not say that he (the father) is carrying the stone], or a basket with a stone in it. [This, on condition that there be fruits in the basket; for if not, it (the basket) is a basis for something forbidden (the stone), and it is forbidden to carry it. And there must also be in it such fruits which, if thrown to the ground, will spoil, such as berries and grapes and the like. But if they were fruits like nuts and almonds, he shakes out the fruits (along with the stone). And with fruits that spoil, too, like berries and grapes, if he can move them to the edge of the basket and shake out the stone alone, it is forbidden to carry it with the stone. Our Mishnah is speaking of an instance in which the sides or the bottom of the basket have eroded to the extent that it is impossible to use the basket without the stone.] And it is permitted to carry unclean terumah together with clean terumah and chullin (mundane food), [but it is forbidden to carry unclean terumah by itself (on Shabbath)]. R. Yehudah says: Meduma (a mixture) may also be brought up with a hundred and one. [If a sa'ah of terumah fell into a hundred sa'ah of chullin, it is permitted to "bring up" the sa'ah of terumah from them on Shabbath so that all remain chullin and permitted to non-Cohanim. And we do not say that he is thereby "correcting" (on Sabbath); for we regard terumah that fell into chullin as lying alone and not being intermixed, so that when it is "brought up" (i.e., when a sa'ah is given to a Cohein from the one hundred and one, it is considered as if the terumah itself which fell into it is brought up, so that there is no "correcting." The halachah is not in accordance with R. Yehudah.]