Vayikra 27:2

כי יפלא means, if he expressly states by an utterance of his mouth (cf. Rashi on Leviticus 22:21). בערכך נפשות — he expressly states that he will give to the Sanctuary the valuation attached to a life by saying, “the payment of the valuation of such and such a thing — that, however, being something upon which its life depends — is incumbent upon me” (Sifra, Bechukotai, Section 3 6; Arakhin 4a).

Speak to the children of Yisra᾽el, and say to them, If a man make a singular vow, to give to the Lord the estimated value of persons,

דַּבֵּ֞ר אֶל־בְּנֵ֤י יִשְׂרָאֵל֙ וְאָמַרְתָּ֣ אֲלֵהֶ֔ם אִ֕ישׁ כִּ֥י יַפְלִ֖א נֶ֑דֶר בְּעֶרְכְּךָ֥ נְפָשֹׁ֖ת לַֽיהֹוָֽה׃