Reference for Bava Batra 241:5

והא ראשי המטות כתיב אמר רב חסדא אמר רבי יוחנן ביחיד מומחה

therefore, had to be taught. What [is meant by] 'the appointed seasons of the Lord were said [but] the annulment of vows was not said [unto them]'? — The [proclamation of the] appointed seasons of the Lord requires [a court of three] qualified mem<span class="x" onmousemove="('comment',' A lay Court of three, or one qualified expert (Mumhe, v. Glos.), has not the right to proclaim the New Moon. ');">¹²</span> [but] the annulment of vows does not require [three] qualified men.<span class="x" onmousemove="('comment',' But a lay Court of three may annul vows. Beth Shammai, also, derives this law in the same way. ');">¹³</span>

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