Reference for Chullin 228:11

אלא אמר מר בריה דרבינא

could prove the reverse: for the fruit is permitted with the fruit and the fruit with the dam is forbidden! Rather said Mar the son of Rabina: Because one can refute the argument thus: A slave, the son of a bondwoman, who is also the brother of a freed bondwoman, could prove otherwise: for the fruit is forbidden with the fruit, nevertheless the fruit with the mother is permitted.<span class="x" onmousemove="('comment',' A slave may not marry a free woman nor a free man a bondwoman. In this case, then, the fruit with the fruit is forbidden, i.e., the slave may not marry the kind of his sister sc. a free woman, but the fruit with the mother is permitted, i.e., the slave may marry the kind of his mother sc. a bondwoman.');">⁸</span>

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