Reference for Sanhedrin 140:15

וטעמא מאי אמר קרא (דברים כא, כ) איננו שומע בקולנו בקולנו ולא בקולו של מקום:

By a RELIGIOUS ACT is meant the meal for comforting mourners;<span class="x" onmousemove="('comment',' Though this was only a Rabbinical enactment. For the earlier clause of the Mishnah IF HE ATE IN A COMPANY (CELEBRATING) A RELIGIOUS ACT might be interpreted as referring to a Biblical precept, e.g the eating of the Passover sacrifice. ');">²²</span> A TRANSGRESSION means eating on a public fast day.<span class="x" onmousemove="('comment',' Proclaimed by Rabbis. Though this too is only a Rabbinical ordinance. ');">²³</span>

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