The commandment of redemption of a Hebrew bondwoman: To redeem a Hebrew bondwoman, as it is stated (Exodus 21:8), “he must let her be redeemed.” And that is a positive commandment, meaning to say that the master that acquired her, help her in her redemption and give her room to go back to the house of her father. [It is] like they, may their memory be blessed, said (Kiddushin 14b), “He reduces the price and she leaves.” [This] means to say that if he took her for [the price of] sixty dinars over six years and she worked three years and gathered thirty dinars, he should take them and send her away. And he should not claim about her that she must finish the years of her bondage regardless, or say, “My money was sitting idly with you; if you want to leave, add the profit to me [that the money should have produced while it was idle]” — as this is only evil-heartedness. And for the Children of Israel who are the children of kings, merciful ones [who are] the children of merciful ones, it is fitting to do kindness with the creatures, even those who serve them, and even [if it is] for one day.
That which we have written about [the previous commandment of] designation (Sefer HaChinukh 43) is from the roots of this commandment. And its details are also there in Kiddushin.
מִצְוַת פִּדְיוֹן אָמָה הָעִבְרִיָּה – לִפְדּוֹת אָמָה הָעִבְרִיָּה, שֶׁנֶּאֱמַר (שמות כא ח) וְהֶפְדָּהּ. וְזוֹ מִצְוַת עֲשֵׂה, כְּלוֹמַר שֶׁיְּסַיֵּעַ הָאָדוֹן הַקּוֹנֶה אוֹתָהּ בְּפִדְיוֹנָהּ וְיִתֵּן לָהּ מָקוֹם לָשׁוּב לְבֵית אָבִיהָ, כְּמוֹ שֶׁאָמְרוּ ז"ל (קדושין יד ב) שֶׁמְּגָרֵעַ פִּדְיוֹנָהּ וְתֵצֵא, כְּלוֹמַר שֶׁאִם לְקָחָהּ בְּשִׁשִּׁים דִּינָרִים לְשֵׁשׁ שָׁנִים וְעָבְדָה שָׁלֹשׁ וְקָמְצָה שְׁלֹשִׁים דִּינָרִים, שֶׁיִּקָּחֵם וִישַׁלְּחֶנָּה וְלֹא יִטְעֹן עָלֶיהָ שֶׁתַּשְׁלִים שְׁנוֹת עֲבוֹדָתָהּ עַל כָּל פָּנִים, אוֹ שֶׁיֹּאמַר מְעוֹתַי הָיוּ בְּטֵלוֹת אֶצְלָהּ, תּוֹסִיף לִי רֶוַח אִם תִּרְצֶה לָצֵאת, שֶׁאֵין זֶה אֶלָּא רֹעַ לֵב, וְלִבְנֵי יִשְׂרָאֵל שֶׁהֵם בְּנֵי מְלָכִים רַחְמָנִים בְּנֵי רַחְמָנִים, רָאוּי לָהֶם לַעֲשׂוֹת חֶסֶד עִם הַבְּרִיּוֹת, אַף כִּי לַאֲשֶׁר עֲבָדוּם, וַאֲפִלּוּ יוֹם אֶחָד.
The commandment of redemption of a Hebrew bondwoman: To redeem a Hebrew bondwoman, as it is stated (Exodus 21:8), “he must let her be redeemed.” And that is a positive commandment, meaning to say that the master that acquired her, help her in her redemption and give her room to go back to the house of her father. [It is] like they, may their memory be blessed, said (Kiddushin 14b), “He reduces the price and she leaves.” [This] means to say that if he took her for [the price of] sixty dinars over six years and she worked three years and gathered thirty dinars, he should take them and send her away. And he should not claim about her that she must finish the years of her bondage regardless, or say, “My money was sitting idly with you; if you want to leave, add the profit to me [that the money should have produced while it was idle]” — as this is only evil-heartedness. And for the Children of Israel who are the children of kings, merciful ones [who are] the children of merciful ones, it is fitting to do kindness with the creatures, even those who serve them, and even [if it is] for one day.
מִשָּׁרְשֵׁי הַמִּצְוָה מָה שֶׁכָּתַבְנוּ בְּיִעוּד, וּפְרָטֶיהָ גַּם כֵּן שָׁם בְּקִדּוּשִׁין.
That which we have written about [the previous commandment of] designation (Sefer HaChinukh 43) is from the roots of this commandment. And its details are also there in Kiddushin.