Positive commandment · Mitzvat Aseh #58 of 613
To eat the meat of the second Paschal offering together with matzot and bitter herbs
לאכול את בשר פסח שני על מצה ומרור
The verse · Bamidbar 9:11
בַּחֹדֶשׁ הַשֵּׁנִי בְּאַרְבָּעָה עָשָׂר יוֹם בֵּין הָעַרְבַּיִם יַעֲשׂוּ אֹתוֹ עַל־מַצּוֹת וּמְרֹרִים יֹאכְלֻהוּ
“On the fourteenth day of the second month at evening they shall keep it, and eat it with unleavened bread and bitter herbs.”
The Rambam’s words
To eat the meat of the second Paschal offering together with matzot and bitter herbs, as [Numbers 9:11] states: "And you shall eat it with matzot and bitter herbs."
לאכול את בשר פסח שני על מצה ומרור, שנאמר: "עַל מַצּוֹת וּמְרוֹרִים יֹאכְלוּהוּ" (במדבר ט, יא).
Why · Sefer HaChinuch #381
The commandment that the second Pesach (Pesach Sheni)-offering be eaten with matzot and marror (bitter herbs)
“From the roots of this commandment are so that the Jews will remember forever the great miracles that G-d performed for them during the exodus from Egypt.”
Who & when
“And [it] is practiced at the time of the [Temple] by males, but not by females.”
Where in the Mishneh Torah
Hilchot Paschal Offering הלכות קרבן פסח