Positive commandment · Mitzvat Aseh #57 of 613
To offer the second Paschal sacrifice
לעשות פסח שני
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 offer the second Paschal sacrifice, as [Numbers 9:11] states: "In the second month, on the fourteenth of the month...."
לעשות פסח שני, שנאמר: "בַּחֹדֶשׁ הַשֵּׁנִי בְּאַרְבָּעָה עָשָׂר" (במדבר ט, יא).
Why · Sefer HaChinuch #380
Second Pesach (Pesach Sheni) on the fourteenth of Iyar
“It is from the roots of the commandment that it is because the commandment of the Pesach-offering is a powerful and clear sign to all of the creation of the world.”
Who & when
“This commandment is practiced at the time of the [Temple] — by males in the category of obligation, and by females in the category of the optional.”
Where in the Mishneh Torah
Hilchot Paschal Offering הלכות קרבן פסח