Shabbos 2:7-3:1

Shabbos 2:7

A man must say three things on Friday at dusk: “Have you separated tithes? Have you prepared the eiruv? Light the lamp!” If it’s unclear whether or not it is yet night, one may not tithe food that is definitely untithed, nor may one immerse utensils in a mikvah or light the lamp but one may tithe food that is doubtfully untithed, prepare the eiruv and insulate hot food.

Shabbos 3:1

If an oven (kirah – comparable to our ovens) is heated using straw or stubble as fuel, one may place a food item on it before Shabbos (because there is no danger that he will rake the straw). If it is heated with peat or wood, he may not place the food on it unless he first removes the coals or puts ashes on them (again, to prevent raking the coals). Beis Shammai say that one may place hot water on the oven but not food; Beis Hillel permit both hot water and food. Beis Shammai say that one may take things from the stovetop but not return them there; Beis Hillel permit one even to return things there.