Ketubot 108A

שוקל לו את שקלו, ופורע את חובו, ומחזיר לו אבידתו. ובמקום שנוטלין שכר ⁠— תפול הנאה להקדש.

the other may contribute his shekel for him, i.e., it is permitted for the second individual to donate the half-shekel from his own money to the Temple on behalf of the first one, who is prohibited by the vow from deriving benefit; and he may repay his debt for him, i.e., if the one prohibited by the vow owes money to a third party, the one from whom he may not derive benefit may pay off that debt on his behalf. And he may return to him his lost object, and in a place where one takes a wage for returning a lost article, the benefit paid for the return of the item goes to the Temple treasury of consecrated property.

בשלמא שוקל לו את שקלו ⁠— מצוה קעביד. דתנן: תורמין על האבוד ועל הגבוי ועל העתיד לגבות.

The Talmud discusses this Mishnah: Granted, he may contribute his shekel for him, as he thereby performs a mitzva. The one prohibited by the vow from deriving benefit does not derive any direct benefit from this action, as even if he did not pay the half-shekel, all Jews have a share in the communal offerings brought in the Temple, as we learned in a baraita: One performs the collection of money from the chamber with the intention that the ceremony apply to money that is lost, and money that has already been gathered but has not yet been brought to the Temple, and money that will be gathered in the future. This shows that even if one did not give a half-shekel, the communal offerings are nevertheless sacrificed in his name.