Reference for Zevachim 8:10
הַנִּתָּנִין מַתָּנָה אַחַת שֶׁנִּתְעָרְבוּ בַנִּתָּנִין בְּמַתָּנָה אַחַת, יִנָּתְנוּ מַתָּנָה אֶחָת. מַתַּן אַרְבַּע בְּמַתַּן אַרְבַּע, יִנָּתְנוּ בְּמַתַּן אַרְבַּע. מַתַּן אַרְבַּע בְּמַתָּנָה אַחַת, רַבִּי אֱלִיעֶזֶר אוֹמֵר, יִנָּתְנוּ בְמַתַּן אַרְבַּע. רַבִּי יְהוֹשֻׁעַ אוֹמֵר, יִנָּתְנוּ בְמַתָּנָה אֶחָת. אָמַר לוֹ רַבִּי אֱלִיעֶזֶר, וַהֲרֵי הוּא עוֹבֵר עַל בַּל תִּגְרַע. אָמַר לוֹ רַבִּי יְהוֹשֻׁעַ, וַהֲרֵי הוּא עוֹבֵר עַל בַּל תּוֹסִיף. אָמַר לוֹ רַבִּי אֱלִיעֶזֶר, לֹא נֶאֱמַר בַּל תּוֹסִיף אֶלָּא כְשֶׁהוּא בְעַצְמוֹ. אָמַר לוֹ רַבִּי יְהוֹשֻׁעַ, לֹא נֶאֱמַר בַּל תִּגְרַע אֶלָּא כְשֶׁהוּא בְעַצְמוֹ. וְעוֹד אָמַר רַבִּי יְהוֹשֻׁעַ, כְּשֶׁנָּתַתָּ, עָבַרְתָּ עַל בַּל תּוֹסִיף וְעָשִׂיתָ מַעֲשֶׂה בְיָדֶךָ. וּכְשֶׁלֹּא נָתַתָּ, עָבַרְתָּ עַל בַּל תִּגְרַע וְלֹא עָשִׂיתָ מַעֲשֶׂה בְיָדֶךָ:
[If] blood that [requires] one application became mixed with [other] blood that [also requires] one application, they [should apply] one application. [If] blood that [requires] four applications [became mixed with blood that requires] four applications, they [should apply] four applications. [If] blood that [requires] four [applications became mixed] with [blood] that [requires] one, Rabbi Eliezer says: They [should apply] four applications. Rabbi Yehoshua says: They [should apply] one application. Rabbi Eliezer said to him [that by doing so] one violates [the commandment of] "Do not detract [from the Torah's commandments]". Rabbi Yehoshua said to him [that by following his approach] one violates [the commandment of] "Do not add [to the Torah's commandments]". Rabbi Eliezer said to him: "Do not add" only applies if it is by itself. Rabbi Yehoshua said to him: "Do not detract" [too] only applies if it is by itself. And Rabbi Yehoshua further said: When you apply [extra] you actively violate "Do not add"; [but] when you do not apply, you violate "Do not detract" but you do it passively.