Parashas Bo · Shemos 12:9 · TT note 18
Torah Temimah on Shemos 12:9, note 18 (on צְלִי אֵשׁ) points to Pesachim 74a.
Sefaria — Exodus 12:9
Sefaria — Torah Temimah on Exodus 12:9
Sefaria — Pesachim 74a
E-Daf — Pesachim 74a
English: And let one bring a metal spit? Because once part of it is hot, all of it is hot, and [the meat] is roasted by the heat of the spit — but the Merciful One said “roasted with fire,” and not roasted by something else.
Practical application of צְלִי אֵשׁ: heat must come from fire, not from a metal conductor.
One may not roast the Pesach on a metal spit, because the spit itself would cook the meat.