After hearing what Sayyidna Ya` qub (علیہ السلام) said, those brothers countered it by saying that his apprehension was strange in view of the presence of a strong group of the ten of them to protect Yusuf. If a wolf could be expected to eat up Yusuf despite their being there to guard him, it would render their very presence around him totally senseless. If so, they could not be taken as good for anything.
Sayyidna Ya` qub (علیہ السلام) acting with the elegance of a great prophet he was, did not say it plainly before his children that it was they about whom he feared a foul play because, firstly it would have been a painful statement to make against all of them and, secondly, there was the danger that such a statement from the father would have increased the en-mity of the brothers to higher proportions - that is, if they somehow abandoned their idea of killing him now, they might have done so at some later occasion under some other excuse. For this reason, he allowed them to go. But, he did make sure that the brothers give him a solemn pledge that they would see that no harm comes to Yusuf. As added pre-caution, he entrusted him with his elder brother Ruebel (Rueben) or Yahuda (Judah) so that they specially take care of his needs there and see that he returns soon and safe. The brothers lifted Yusuf up on their shoulders, and kept doing so one by one. Sayyidna Yaqui followed them upto a certain distance to bid them farewell.
When these people, as described by Al-Qurtubi following historical narrations, disappeared from the sight of Sayyidna Ya` qub (علیہ السلام) ، the brother on whose shoulders Sayyidna Yusuf (علیہ السلام) was perched threw him down on the ground. He started walking by himself. But, being too small, he could not keep pace with them and tried to seek help from another brother. He remained cold. So did every brother he went to for help. They told him that he better call for help those eleven stars, the Sun and the Moon he had seen prostrating to him - they should help him.
From here, Al-Qurtubi concludes that the brothers had somehow found out about the dream of Sayyidna Yusuf ill. That dream became the cause of their extreme hostility.
Finally, Sayyidna Yusuf (علیہ السلام) appealed to Yahuda as his elder brother telling him about his plight. He was weak and small and needed protection, at least for the sake of their old father to whom they had given the pledge to help him. Yahuda was moved and he told him that until he was alive, he would not let these brothers hurt him.
Thus, when Allah Ta` ala put mercy in the heart of Yahuda and the ability to do what was right, he told the other brothers of his that killing someone sinless was an extremely grave sin, therefore, they should fear Allah and take the innocent child back to his father. However, to make things easy on them, they could take a pledge from him that he would not complain to him in any way about their behaviour.
The brothers told Yahuda: We know what you mean. You wish to rise higher than us in the sight of our father. So, you better listen to us. If you do anything to resist our intention, we shall kill you too. When Yahuda realized that he alone could do nothing against his nine brothers, he told them: Well, if you have decided to get rid of this child, then, listen to me carefully. There is an old well nearby with a lot of wild growth in it and now a home for many lethal crawlers. Put him in that well. If a snake or scorpion bites and kills him there, you shall have what you are looking for. Thus, you shall remain free of the blame of shedding his blood by your own hands. And, in case, he still remains alive, then, may be there comes a caravan this way, lowers its bucket to draw water from it and finds him instead. It is likely that they would take him away with them to some other country in which case too you would have achieved your objective.