Negative commandment · Lo Ta’aseh #155 of 613
Not to delay his vows for more than three festivals
שלא לאחר הנדרים והנדבות שנדר ושנדב
The verse · Devarim 23:22
כִּי־תִדֹּר נֶדֶר לַה׳ אֱלֹהֶיךָ לֹא תְאַחֵר לְשַׁלְּמוֹ כִּי־דָרֹשׁ יִדְרְשֶׁנּוּ ה׳ אֱלֹהֶיךָ מֵעִמָּךְ וְהָיָה בְךָ חֵטְא
“When thou shalt vow a vow to the Lord thy God, thou shalt not be slack to pay it: for the Lord thy God will surely require it of thee; and it would be sin in thee.”
The Rambam’s words
Not to delay bringing sacrifices you have vowed to offer, or animals which you have pledged to bring as sacrifices, as [Deuteronomy 23:22] states: "[When you make a pledge to G-d,] do not delay paying it."
שלא לאחר הנדרים והנדבות שנדר ושנדב, שנאמר "לא תאחר לשלמו" (דברים כג,כב).
Where in the Mishneh Torah
Hilchot Sacrificial Procedure הלכות מעשה הקרבנות