פּירוש אויף שמות 10:9

...

כי חג לה' לנו, “for we celebrate a festival in honour of the Lord;” it is customary to celebrate festivals in the presence of wife and children.

כי חג ה' לנו, “for it is a festival of Hashem for us.” The festival Moses and Aaron spoke about was the holiday of Shavuot, the day the Torah would be given. G’d had already advised Moses of that event when He had told him at the burning bush: “when you take out the people from Egypt you will serve Me at this Mountain” (3,12). The festival Moses spoke of is not to be understood as the festival of Passover; the Passover was observed inside Egypt. It is also impossible to understand the word חג Moses spoke about as the festival of Tabernacles as nowhere is that festival connected to the Mountain of G’d. There is no doubt therefore, that the festival in question is Shavuot which occurs in the month of Sivan. The Torah writes: “in the third month after the Exodus of the Children of Israel from Egypt they arrived in the desert of Sinai.” The date mentioned there was the first day of Sivan (Shabbat 19). After an interval of five days the Torah (Ten Commandments) were given at Mount Sinai.