Musar for Sanhedrin 162:13
<big><strong>מתני׳</strong></big> ההורג נפש שלא בעדים מכניסין אותו לכיפה ומאכילין אותו (ישעיהו ל, כ) לחם צר ומים לחץ:
that only flagellation affords it. But what of the following that has been taught, viz.: If he [the transgressor] was warned [of his liability to flagellation], but remained silent, or warned and nodded his head, — the first and second time he is to be warned, but on the third occasion he is placed in a cell. Abba Saul said: The third time too he is warned, but on the fourth, he is placed in a cell.<span class="x" onmousemove="('comment',' Tosef. XII. When a warning is given, the offender must explicitly accept it, (cf. supra pp. 494-5), otherwise he cannot be punished. Nevertheless, since he was warned, and shewed by his silence or his nodding that he accepted the warning, there is a presumption that he is a confirmed sinner, and hence the law of Mishnah applies to him. ');"><sup>11</sup></span>