Reference for Keritot 49:52

אי ס"ד חובה היא מתיידע ליה אמאי מייתי חטאת

The [other] Rabbis on the other hand say: Burnt-offerings and peace-offerings may be brought either in fulfilment of a vow or as freewill sacrifices,<span class="x" onmousemove="('comment',' Heb. neder or nedabah. In the latter a particular animal is dedicated, in the former a sacrifice generally is vowed.');">³³</span>

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