Genesis Rabbah, 4:6

“And God made the expanse, and it separated the water that was below the expanse from the water that was above the expanse. And it was so. God called the expanse ‘sky.’ And there was evening and there was morning, a second day.” (Genesis 1:7-8) Why is it that “it was good” is not written in connection with the second day? Rabbi Yochanan said, and it was also taught in the name of Rabbi Yosi ben R. Halafta, “Because on that day, Gehinnom [a source of punishment in the afterlife] was created.”. . .Rabbi Chanina said, “Because on that day, a schism was created, as it is written, “let it divide the waters.” R. Tavyomi said, “If because of a division made l’taken olam and to stabilize it, ‘it was good’ is not written in connection with that day, how much more so should this apply to a schism that leads to the confusion of the world. [Translation by Rabbi Jill Jacobs]