Parashas Vaeira · Passuk 6:13
Chabad.org — English translation + Rashi
Torah Temimah points to Yerushalmi 3:5 (verified).
English: “Rabbi Shmuel bar Rav Yitzchak said: What did God command them about? About the section concerning the freeing of slaves. This accords with Rabbi Hila, who said that Israel were punished because of the matter of releasing slaves.”
On the daf / in context: See the cited source for the full section.
Yerushalmi interpretation of the command concerning Israel
Chazal understand the otherwise unspecified command to the Israelites as including the obligation to release Hebrew slaves, connecting it with the later rebuke over that law.