Reference for Bekhorot 119:3

אלא כונסן לדיר ומוציא עשרה ונוטל מהן אחד והשאר מצטרפין לגורן אחר

into the shed, bring out ten, take one from them [as tithe], and the rest combine with those of a later tithing period.<span class="x" onmousemove="('comment',' We are therefore taught here two things. First, that he cannot select the meagre ones alone to be tithed, and again, that, although only five lambs remain, he cannot say that they are altogether exempt but must combine them with those born at a later tithing period.');">²</span>

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