Reference for Chullin 269:46

אפ"ה פשטה קדושה בכולה

And the Rabbis? - [They say that] it serves to exclude only that which is held jointly with a gentile.<span class="x" onmousemove="('comment',' But that which is held by two Israelites jointly is subject to the law of the first of the fleece, since each is individually subject to the law, and the people of Israel are often referred to as a single individual; cf. Mak. 23b.');"><sup>25</sup></span>