Reference for Chullin 271:52

אי מה תרומה מחדש על הישן לא אף ראשית הגז מחדש על הישן לא

so in the case of the first of the fleece one should not give new [fleece as the due] for old? - This is indeed so; for it has been taught: If a man had two lambs and he sheared them and kept [the wool], and [next year] again sheared them and kept [the wool], and so he did for two or three years, they are not to be reckoned together.<span class="x" onmousemove="('comment',' Even though he has now accumulated five fleeces; for there must be five fleeces from five sheep.');">³⁷</span>

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