כִּֽי־תִדֹּ֥ר נֶ֙דֶר֙ לַיהוָ֣ה אֱלֹהֶ֔יךָ לֹ֥א תְאַחֵ֖ר לְשַׁלְּמ֑וֹ כִּֽי־דָּרֹ֨שׁ יִדְרְשֶׁ֜נּוּ יְהוָ֤ה אֱלֹהֶ֙יךָ֙ מֵֽעִמָּ֔ךְ וְהָיָ֥ה בְךָ֖ חֵֽטְא׃
Quand tu auras fait un vœu à l’Éternel, ton Dieu, ne tarde point à l’accomplir; autrement, l’Éternel, ton Dieu, ne manquerait pas de t’en demander compte, et tu aurais à répondre d’un péché.
Rashi
לא תאחר לשלמו [WHEN THOU SHALT VOW A VOW UNTO THE LORD THY GOD] THOU SHALT NOT DELAY TO PAY IT — beyond three festivals after the vow has been made. Our Rabbis have deduced it (the fact that one does not transgress the prohibition before three festivals elapse) from a Scriptural text (Rosh Hashanah 4b).
Chizkuni
כי תדור נדר, “When you shall vow a vow, etc.” It is possible that this verse appears here as we read previously (verse 19) about a harlot not being allowed to fulfill a vow she had made to the Lord by using money earned from practicing her trade.
Ibn Ezra
Having mentioned the prohibition of “the earnings of a harlot … for any vow” [: 19], Scripture now discusses the case of when you vow a donation.