Rhys Davids: 'If it is not disagreeable to you, Kassapa, let me spend one night in the room where your (sacred) fire is kept.'
IB Horner/Brahmali: “If it is not inconvenient to you, Kassapa, let me stay for one night in the fire-room.”
U Hla Myint (see Online Pali Courses) : “If to you, Kassapa, not troublesome, we would like to stay for one night in the kitchen.”
Looking at dictionary entries (on SuttaCentral):
agyāgāra m. a hut for the (ritual) fire(s).
(So far the first 2 translations still sound okay, the 3rd is weird.)
This is a technical term in brahmanical ritual. It refers to a room, chamber, or shrine where the sacred fire is tended and worshiped. It occurs several times in the suttas, always in the same sense. The Buddha frequently stayed in shrines and sacred places, for example the cetiyas which were tree-shrines, and it seems that sometimes he stayed in the fire-chamber.
In DN 3, for example, we find:
Furthermore, take some ascetic or brahmin who, not managing to obtain this supreme knowledge and conduct, or to get by eating fallen fruit, or to get by eating tubers and fruit, sets up a fire chamber (agyāgāraṃ karitvā) in the neighborhood of a village or town and dwells there serving the sacred flame.
Hmmm… if you replace it with kitchen then the whole passage is somehow saying the ascetic or brahmin ends up becoming either a cook or a householder, cooking for himself?
