Reference for Shabbat 136:1
אבל לא שכחה מאי חייב על כל מלאכה ומלאכה אדתני היודע שהוא שבת ועשה מלאכות הרבה בשבתות הרבה חייב על כל מלאכה ומלאכה ליתני היודע עיקר שבת וכל שכן הא אלא מתניתין כשהכיר ולבסוף שכח ודרב ושמואל נמי כהכיר ולבסוף שכח דמי והכי איתמר רב ושמואל דאמרי תרוייהו אפילו תינוק שנשבה בין הנכרים וגר שנתגייר לבין הנכרים כהכיר ולבסוף שכח דמי וחייב
What if he did not forget it?<span class="x" onmousemove="('comment',' Sc. the essential law of the Sabbath, but merely that that particular day was the Sabbath. ');"><sup>1</sup></span> He is liable for each labour? Then instead of teaching, HE WHO KNOWS THAT IT IS THE SABBATH AND PERFORMS MANY LABOURS ON MANY SABBATHS, IS LIABLE FOR EVERY LABOUR, let him teach, He who knows the essential law of the Sabbath, and how much more so this case? Rather our Mishnah refers to one who knew but subsequently forgot, and Rab and Samuel's [ruling] too is similar to the case of one who knew but subsequently forgot, and it was thus stated: Rab and Samuel both maintain: Even a child who was taken captive among Gentiles or a proselyte who became converted in the midst of Gentiles is as one who knew but subsequently forgot, and so he is liable. But R. Johanan and Resh Lakish maintain: Only one who knew but subsequently forgot [is liable], but a child who was taken captive among Gentiles, or a proselyte who became converted in the midst of Gentiles, is not culpable.