Reference for Kilayim 8:3

הַמַּנְהִיג סוֹפֵג אֶת הָאַרְבָּעִים, וְהַיּוֹשֵׁב בַּקָּרוֹן סוֹפֵג אֶת הָאַרְבָּעִים. רַבִּי מֵאִיר פּוֹטֵר. וְהַשְּׁלִישִׁית שֶׁהִיא קְשׁוּרָה לָרְצוּעוֹת, אֲסוּרָה:

If one drives [a mixture of two species of animals] receives forty [lashes] and the one who sits in the wagon [being pulled by the mixture] receives forty [lashes]. Rabbi Meir exempts [the one sitting in the wagon]. If a third animal [of a different species] is tied to the straps [of a wagon drawn by two animals of the same species] it is prohibited.

Jastrow

Jastrow