Positive commandment · Mitzvat Aseh #83 of 613
That one brings all of his vows on the first festival
להביא כל הקרבנות שיש על האדם בחובה או בנדבה ברגל ראשון שפגע בו
The verse · Devarim 12:5
כִּי אִם־אֶל־הַמָּקוֹם אֲשֶׁר־יִבְחַר ה׳ אֱלֹהֵיכֶם מִכׇּל־שִׁבְטֵיכֶם לָשׂוּם אֶת־שְׁמוֹ שָׁם לְשִׁכְנוֹ תִדְרְשׁוּ וּבָאתָ שָּׁמָּה
“But to the place which the Lord your God shall choose out of all your tribes to put his name there, there shall you seek him, at his dwelling, and there shalt thou come:”
The Rambam’s words
For a person to bring all the sacrifices for which he is liable, be they obligatory or voluntary offerings, on the first pilgrimage festival that occurs, as [Deuteronomy 12:5-6] states: "And you shall come there... and you shall bring there...."
להביא כל הקרבנות שיש על האדם בחובה או בנדבה ברגל ראשון שפגע בו, שנאמר: "ובאת שמה" (דברים יב,ה), "והבאתם שמה" (דברים יב,ו).
Why · Sefer HaChinuch #438
That one brings all of his vows on the first festival
“It is from the roots of the commandment [that it is] because it is not fitting for a person to be lazy about that which he has vowed to do for a commandment, as is well-known among people.”
Who & when
“And this commandment is practiced at the time of the [Temple], as we had permission then to do vows and promises and there was a place for us to sacrifice [them].”
Where in the Mishneh Torah
Hilchot Sacrificial Procedure הלכות מעשה הקרבנות