Reference for Temurah 6:2

אֵיזֶהוּ אֶתְנָן. הָאוֹמֵר לְזוֹנָה, הֵא לִיךְ טָלֶה זֶה בִשְׂכָרֵךְ, אֲפִלּוּ מֵאָה, כֻּלָּן אֲסוּרִין. וְכֵן הָאוֹמֵר לַחֲבֵרוֹ, הֵא לְךָ טָלֶה זֶה וְתָלִין שִׁפְחָתְךָ אֵצֶל עַבְדִּי, רַבִּי אוֹמֵר, אֵינוֹ אֶתְנָן. וַחֲכָמִים אוֹמְרִים, אֶתְנָן:

What is a prostitute's fee? One says to a prostitute, "Take this lamb as your payment." Even [if he gave her] one hundred [lambs], they are all forbidden. So too is the one who says to his friend, "Take this lamb and your maidservant will sleep with my slave," Rebbe says, "This is not a prostitute's payment." The Sages say, "It is a prostitute's payment."

Jastrow