(Zeus) hid fire; but that the noble son of Iapetos stole again for men from Zeus the counselor in a hollow fennel-stalk, so that Zeus who delights in thunder did not see it. (Hesiod W&D) But what was the source of the fire that Prometheus (son of Iapetus) stole from the gods. Suggestions are from the forge of Hephaestus or the charior to Helios. Being inspired by the references below I suggest the former. Let me point out that in Greek Epic “Hephaestus”, the name of the smithy god, son of Zeus is often a synonym of “fire”.
(Dionysius) raising high the fiery flame from the pine torch bursts forth from the stalk [narthēx],” (Bacchae 145-147) “Dionysus literally ignites the singing and the dancing as he leaps out, in an elemental burst of flame, from inside the fennel stalk or narthēx “ (The Ancient Greek Hero in 24 Hours; 21.50)
Hephaestus refused to listen to any other of the gods save Dionysus -- in him he reposed the fullest trust - and after making him drunk Dionysus brought him to heaven."( Pausanias, Description of Greece 1. 20. 2-3)
In summary; Prometheus steals the fire and Dionysius returns it.