Reference for Sanhedrin 162:15

ורב חסדא אמר אבימי כגון דאיתכחוש בבדיקות ולא איתכחוש בחקירות כדתנן מעשה ובדק בן זכאי בעוקצי תאנים:

wherein then do they differ? — Rabina said: They differ as to whether one must be warned of the cell.<span class="x" onmousemove="('comment',' Both agree that he becomes a confirmed sinner when he has thrice transgressed. The first Tanna maintains that once we regard him as such, he is placed in a cell without further ado; but Abba Saul is of the opinion that this too must be preceded by a formal warning. Hence, after sinning three times, it is necessary that he shall sin a fourth time, that he may be warned of the consequences. ');">¹³</span>

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