Reference for Niddah 29:27

ושמואל אמר

on the ground that the man has experienced an emission of semen? — This is a case where his intercourse was not consummated.<span class="x" onmousemove="('comment',' R. Akiba, however, maintains that the first stage of intercourse with a menstruant is regarded as its consummation, and consequently uncleanness is conveyed even in such a case (Rashi). ');">²⁵</span>

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