Numbers 29:39

אלה תעשו לה׳ במועדיכם THESE YE SHALL OFFER TO THE LORD ON YOUR APPOINTED FESTIVALS — as something that is laid down as a duty, לבד מנדריכם BESIDES YOUR VOWS [AND YOUR FREEWILL OFFERINGS] — If on the Festival you wish to make a vow to bring a sacrifice, you have a duty ready at hand to your credit and you should bring it on that Festival; or in the case of vow-offerings and freewill offerings which you have vowed all the year, bring them on the Festival. — Perhaps it will be difficult for one to go up again to Jerusalem to bring his vow-offerings, and consequently he will transgress the command, (Deuteronomy 23:22) “Thou shalt not delay to pay it (thy vow)”.

אֵ֛לֶּה תַּעֲשׂ֥וּ לַיהֹוָ֖ה בְּמוֹעֲדֵיכֶ֑ם לְבַ֨ד מִנִּדְרֵיכֶ֜ם וְנִדְבֹתֵיכֶ֗ם לְעֹלֹֽתֵיכֶם֙ וּלְמִנְחֹ֣תֵיכֶ֔ם וּלְנִסְכֵּיכֶ֖ם וּלְשַׁלְמֵיכֶֽם׃

These things you shall do to the Lord in your set feasts, besides your vows, and your freewill offerings, for your burnt offerings, and for your meal offerings, and for your drink offerings, and for your peace offerings.