Positive commandment · Mitzvat Aseh #214 of 613
For a groom to rejoice together with his wife for a year
לשמח חתן את אשתו שנה
The verse · Devarim 24:5
כִּי־יִקַּח אִישׁ אִשָּׁה חֲדָשָׁה לֹא יֵצֵא בַּצָּבָא וְלֹא־יַעֲבֹר עָלָיו לְכׇל־דָּבָר נָקִי יִהְיֶה לְבֵיתוֹ שָׁנָה אֶחָת וְשִׂמַּח אֶת־אִשְׁתּוֹ אֲשֶׁר־לָקָח
“When a man has taken a new wife, he shall not go out to war, neither shall he be charged with any business: but he shall be free at home one year, and shall cheer his wife whom he has taken.”
The Rambam’s words
For a groom to rejoice together with his wife for a year, as [Deuteronomy 24:5] states: "He shall be free for his home for one year."
לשמח חתן את אשתו שנה, שנאמר: "נקי יהיה לביתו שנה אחת" (דברים כד, ה).
Why · Sefer HaChinuch #582
The commandment that a groom rejoice with his wife for one year
“It is from the roots of the commandment that G-d, may He be blessed, had it come up in thought in front of Him to create the world; and His desire was that it be inhabited with good creatures born from male and female that mate properly — as licentiousness is an abomination in front of Him.”
Who & when
“And this commandment, regarding that the people of the city not force him to go to war, is practiced at the time of the [Temple], as then we would sometimes go out to war.”
Where in the Mishneh Torah
Hilchot Kings and Wars הלכות מלכים ומלחמות