Positive commandment · Mitzvat Aseh #19 of 613
To bless [G-d] after eating
לְבָרַךְ אַחַר הַמָּזוֹן
The verse · Devarim 8:10
וְאָכַלְתָּ וְשָׂבָעְתָּ וּבֵרַכְתָּ אֶת־ה׳ אֱלֹהֶיךָ עַל־הָאָרֶץ הַטֹּבָה אֲשֶׁר נָתַן־לָךְ
“When thou hast eaten and art replete, then thou shalt bless the Lord thy God for the good land which he has given thee.”
The Rambam’s words
To bless [G-d] after eating, as [Deuteronomy 8:10] states: "[After] you eat and are satisfied, you shall bless G-d, your Lord."
לְבָרַךְ אַחַר הַמָּזוֹן, שֶׁנֶּאֱמָר: "וְאָכַלְתָּ וְשָׂבָעְתָּ וּבֵרַכְתָּ אֶת יְיָ אֱלֹהֶיךָ" (דברים ח, י).
Why · Sefer HaChinuch #430
Birkat HaMazon: blessing Hashem after eating
“From the roots of the commandment, [there is a need to] preface that, have I not told you my son, in what has preceded, that all glory, all majesty, all the good, all wisdom, all power and blessing are of G-d, blessed be He.”
Who & when
“And this commandment is practiced by Torah writ in every place and at all times by males.”
Where in the Mishneh Torah
Hilchot Blessings הלכות ברכות