Reference for Yoma 40:1

ואי סלקא דעתך מחצות דאורייתא היא היכי מקדמינן (והיכי מאחרינן)

if the thought should arise in you that midnight is a time fixed by the Torah, how could it be anticipated [or postponed]?<span class="x" onmousemove="('comment',' [Since before midnight it is not considered consumed. Rashi omits 'or postponed' which is bracketed in cur. edd. Tosaf. retains it explaining it on the principle that 'the zealous perform a religious duty as early as possible'.]');">¹</span> - Rather said R'Johanan: By mere logical conclusion from the text 'All the night' would I not know that it means until the morning, why then the teaching 'until the morning'? Add another morning to the 'morning of the night',<span class="x" onmousemove="('comment',' The morning of the night' is the dawn. The additional morning is the margin of before and after the cockcrow.');">²</span>

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