פירוש על עבודה זרה 32:9

Zera begins his adventure by learning at the school of R. Judah. There he learns the statement, but Rav Judah does not know whether he learned it from Shmuel or from Rav, the two great amoraim of the first generation in Babylonia.
At Korkunia, he hears another sage reciting the tradition in the name of Shmuel, so he believes that it originated with him.