Shabbat 20A

ובגבולין, כדי שתאחוז האור ברובו. רבי יהודה אומר: בפחמין ⁠— כל שהוא.

And, however, in the outlying areas, meaning in all of Eretz Yisrael outside the Temple, it is prohibited to light a bonfire on Friday, unless there is sufficient time for the fire to take hold in most of the bonfire, while it is still day. R' Yehuda says: With a bonfire of coals, even in the outlying areas one is permitted to light the fire on Friday at nightfall, even if the fire only spread to any amount of the bonfire. The coals, once they are kindled, will not be extinguished again, and there is no concern lest he come to tend to them on Shabbat.

גמ׳ וכמה? אמר רבי אלעזר אמר רב: כדי שיצולו מבעוד יום כמאכל בן דרוסאי. איתמר נמי, אמר רב אסי אמר רבי יוחנן: כל שהוא כמאכל בן דרוסאי, אין בו משום בישולי גוים. תניא חנניא אומר: כל שהוא כמאכל בן דרוסאי ⁠— מותר להשהותו על גבי כירה ואף על פי שאין גרופה וקטומה.

Talmud: We learned in the Mishnah that one may only roast meat and other food items if there remains sufficient time so that they could be roasted while it is still day. The Talmud asks: And how much do they need to be roasted in order to be considered sufficient, so that it will be permitted to complete their cooking afterward? R' Elazar said that Rav said: So that they will be roasted while it is still day like the food of ben Drosai, which was partially roasted. Ben Drosai was a robber and pursued by all. He could not wait for his food to roast completely, so he sufficed with a partial roasting. It was also stated by another of the rabbis, as Rav Asi said that R' Yoḥanan said: Anything that is already cooked like the food of ben Drosai by a Jew, no longer has a problem of the cooking of non-Jews. If a non-Jew completed cooking this food, it is, nevertheless, permitted to eat, even though, as a rule, it is prohibited to eat food cooked by non-Jews. It was taught in a baraita, Ḥananya says: With regard to anything that is already cooked like the food of ben Drosai, it is permitted to keep it on the stove on Shabbat and even though this stove is not swept of coals and the burning coals are not covered with ashes. Since the food was already cooked to that extent, there is no concern that he will come to stoke the coals.