Philo Judaeus De Josepho 15

But on that day it happened by some chance that certain merchants who were accustomed to convey their merchandise from Arabia to Egypt were travelling that way, and so the eleven brethren drew Joseph up out of the pit and sold him to them; the one of them who was the fourth in respect of age instigating this contrivance; for in my opinion, he was afraid lest his brother might be treacherously slain by the others, who had conceived an irreconcilable hatred against him, and therefore he proposed that he should be sold, substituting slavery for death, the lighter evil for the greater.