Reference for Arakhin 5:1
הָאוֹמֵר, מִשְׁקָלִי עָלָי, נוֹתֵן מִשְׁקָלוֹ. אִם כֶּסֶף, כֶּסֶף. אִם זָהָב, זָהָב. מַעֲשֶׂה בְּאִמָּהּ שֶׁל יִרְמַטְיָה שֶׁאָמְרָה, מִשְׁקַל בִּתִּי עָלָי, וְעָלְתָה לִירוּשָׁלַיִם, וּשְׁקָלוּהָ וְנָתְנָה מִשְׁקָלָהּ זָהָב. מִשְׁקַל יָדִי עָלָי, רַבִּי יְהוּדָה אוֹמֵר, מְמַלֵּא חָבִית מַיִם וּמַכְנִיסָהּ עַד מַרְפֵּקוֹ, וְשׁוֹקֵל בְּשַׂר חֲמוֹר וְגִידִין וַעֲצָמוֹת וְנוֹתֵן לְתוֹכָהּ עַד שֶׁתִּתְמַלֵּא. אָמַר רַבִּי יוֹסֵי, וְכִי הֵיאַךְ אֶפְשָׁר לְכַוֵּן בָּשָׂר כְּנֶגֶד בָּשָׂר וַעֲצָמוֹת כְּנֶגֶד עֲצָמוֹת. אֶלָּא שָׁמִין אֶת הַיָּד כַּמָּה הִיא רְאוּיָה לִשְׁקֹל:
One who said, “I vow my weight,” he must give his weight, if [he said] silver, in silver; if [he said] gold, in gold. It happened with the mother of Yirmatia, who said, “I vow my daughter's weight.” She went up to Jerusalem and weighed her and then gave her weight in gold. [If a man said, “I vow] the weight of my hand,”Rabbi Judah says: let him fill a barrel with water and put it [his hand] in up to the elbow. Then let him weigh the flesh, bones and sinews of a donkey and put it into the barrel until it is filled up again; Rabbi Yose said: “Is it possible to account exactly one kind of flesh against another kind of flesh, and one kind of bones against another kind of bones? Rather, one estimates what the hand is likely to weigh.