Reference for Zevachim 11:3
נִתַּז מִן הַצַּוָּאר עַל הַבֶּגֶד, אֵינוֹ טָעוּן כִּבּוּס. מִן הַקֶּרֶן וּמִן הַיְסוֹד, אֵינוֹ טָעוּן כִּבּוּס. נִשְׁפַּךְ עַל הָרִצְפָּה וַאֲסָפוֹ, אֵינוֹ טָעוּן כִּבּוּס. אֵין טָעוּן כִּבּוּס אֶלָּא הַדָּם שֶׁנִּתְקַבֵּל בִּכְלִי וְרָאוּי לְהַזָּיָה. נִתַּז עַל הָעוֹר עַד שֶׁלֹּא הֻפְשַׁט, אֵינוֹ טָעוּן כִּבּוּס. מִשֶּׁהֻפְשַׁט, טָעוּן כִּבּוּס, דִּבְרֵי רַבִּי יְהוּדָה. רַבִּי אֱלִיעֶזֶר אוֹמֵר, אַף מִשֶּׁהֻפְשַׁט אֵינוֹ טָעוּן כִּבּוּס. אֵינוֹ טָעוּן כִּבּוּס אֶלָּא מְקוֹם הַדָּם, וְדָבָר שֶׁהוּא רָאוּי לְקַבֵּל טֻמְאָה, וְרָאוּי לְכִבּוּס:
[If] blood splattered from the neck onto clothing, it does not require washing. [If it splattered] off the corner [of the altar] or off the base [of the altar], it does not require washing. If it spilled on the floor and he [the priest] gathered it, it does not require washing. Blood only requires washing if it was collected in a vessel and was valid for dashing [against the altar]. [If] it splattered onto the hide before [the latter] was removed [from the animal] it does not require washing; [if it splattered] after it was removed it does require washing - [these are] the words of Rabbi Yehudah; Rabbi Eliezer says: Even after it was removed it does not require washing. Only the spot where blood [was splattered] requires washing. [Only] something subject to impurity [must be washed]; [only] something that can be washed [need be washed].