Fa-in lam ta'toonee bihi fala kayla lakum AAindee wala taqraboon (surah Yusuf: 60)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(12:60) But if you do not bring him to me you shall have no grain from me: nay you should not even come near me. " *52

Fa il lam taatoonee bihee falaa kaila lakum `indee wa laa taqraboon

*52) As the Qur'an has omitted the details, someone might be at a loss to know as to how he brought Benjamin into the conversation with his brothers, and why he insisted on them to bring him with them, when he intended to keep his own identity secret from them. For, obviously these things might have led to the revelation of that secret. But a little thinking will show that he could have very easily and naturally led the conversation up to Benjamin without arousing their curiosity. As there were strict restrictions on the purchase of corn, everyone was permitted to buy only a fixed quantity of it. Most probably the ten brothers had applied for corn for their father and the eleventh brother as well. At this Prophet Joseph might have asked the reason why their father and brother had not personally come for it. Then he might have accepted the excuse for their father that he was old and blind but he would have expressed his doubts about their excuse for their brother that he was their step-brother and the father would not send him with them and so forth. Then he might have declared, "Well, this time we give you as much corn as you have asked for, but the next time you come here you should bring your step-brother with you; otherwise you will not get any corn at all because of this false statement of yours." Along with this threat, he tried to win them over by reminding them of his liberal and generous treatment with them, because he yearned for the sight of his younger brother, and was anxious to know how his family had fared during his absence.
The above is a simple and natural explanation of the matter. Thus this part of the story as given in the Bible (Gen. chapters 42 and 43) appears to be farfetched, exaggerated, unreal and, therefore, un-reliable.