Reference for Niddah 126:19

את אמריתה ניהלן ואהא אמריתה ניהלן

And in connection with this you told us: Rab Judah citing Samuel stated, This is the view of R. Gamaliel son of Rabbi who cited it in the name of R. Simeon b. Gamaliel,<span class="x" onmousemove="('comment',' Who holds that presumption cannot be established unless an occurrence was repeated three times (cf. Yeb. 64b). ');">¹⁷</span>

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