Yechiel Michel Epstein,
Translation:Arukh ha-Shulchan…
“ Section 18 It is widely know that the obligation to eat Matzah exists only on the first night, as the verse states: "In the evening you shall eat Matzah". If one wishes to avoid Matzah for the remainder of the festival he may do so. It is only on Shabbos and the actual Yom Tov days [when work is prohibited] when one must eat bread - which on Pesach would have to be Matzah [as bread is prohibited] - though this would not be due to any positive obligation to eat Matzah. Even on the first night itself one is only required by the Torah to eat an olive-sized piece. ”
