Reference for Yoma 96:1

חישב בחתיית גחלים מהו מכשירי מצוה כמצוה דמו או לא תיקו

If he, in removing the coals [for the incense], had an unlawful intention - what then? Are preliminary<span class="x" onmousemove="('comment',' So that his unlawful thought in connection with the preliminary act would have the same effect as such thought in connection with the religious act in itself and so the incense is rendered invalidated. Another interpretation would limit the effects of his unlawful intention to the preliminary act, here to the embers.');">¹</span>

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