Midrasch zu Bereschit 37:16

And (Gabriel) said to him: What seekest thou? He said to him: I seek my brethren, as it is said, "And he said, I seek my brethren" (Gen. 37:16). And he led him to || his brethren, and they saw him and sought to slay him, as it is said, "And they saw him afar off" (Gen. 37:18). Reuben said to them: Do not shed his blood, as it is said, "And Reuben said unto them, Shed no blood; cast him into this pit that is in the wilderness" (Gen. 37:22). And his brethren listened to him, and they took Joseph and cast him into the pit, as it is said, "And they took him, and cast him into the pit" (Gen. 37:24). What did Reuben do? He went and stayed on one of the mountains, so as to go down by night to bring up Joseph out of the pit. And his nine brethren were sitting down in one place, all of them like one man, with one heart and one plan. Ishmaelites passed by them, and (the brethren) said: Come, let us sell him to the Ishmaelites, and they will lead him to the end of the wilderness, and Jacob will not hear any further report concerning him.