הלכה על שבת 47:12

And they, may their memory be blessed, obligated us (Shabbat 24a) to mention the holiness of the day in the Grace after Meals, meaning to say the matter of Shabbat or holidays, as is known. And on the days that a person is obligated to eat [a meal] regardless, we make one that forgot and did not mention it in the blessing go back; and these are the two obligatory meals, which are the first night of Pesach and the first night of the holiday of Sukkot. And the opinion of some commentators is that we also make him go back on every Shabbat and every holiday.