When were the Jewish people commanded the mitzvah of honoring one’s parents?
The Jewish people were commanded the mitzvah of honoring one’s parents when they encamped in Marah and were given several commands. [This occurred several weeks prior to Matan Torah, as they encamped in Marah after traveling for three days after they crossed the Yam Suf.] This is hinted to in the words “Kasher Tzivcha Hasehm Elokecha” which is written in the 10 Commandments, and implies that we were already commanded this mitzvah, as indeed we were previously commanded it during our stay in Marah.
 Braisa Sanhedrin 56b; Seder Olam Raba 5; Rashi Mishpatim 24:3; Beshalach 15:25; Vaeschanon 5:16; Likkutei Sichos 5:147, 153-154; Encyclopedia Talmudit Erech Kibud Av Vaeim Vol. 26 p. 375-376
 See beshalach 15:25 “Sham Sam Lo Chok Umishpat” and Rebbe Yehuda in Sanhedrin ibid says that Mihspat here refers to Kibbud Av Vaeim
 See Beshalach 15:22