Rabbi Bena’ah, son of Rav Ulla, said: Why was “ki tov” not said on the second day of the week? Because the light of Gehinom was created on that day.
On the daf / in context: The teaching explains the absence of “ki tov” in the account of the second day by connecting that day with the creation of Gehinom.
Type of Learning: Explaining an omitted phrase in the creation accountWhat Is Learned: The missing “ki tov” on the second day is explained through the teaching that the light of Gehinom was created then.