Parashas Vayakhel · Passuk 35:3
Torah Temimah points to classical source on this unit (verified).
English: “On the Shabbos day” — you may not kindle on Shabbos, but you may kindle on Friday for Shabbos.
Derash limiting the prohibition to kindling performed on Shabbos itself.
The prohibition concerns performing the act of kindling on Shabbos itself; a fire kindled before Shabbos may continue burning into Shabbos.