قالوا إن يسرق فقد سرق أخ له من قبل فأسرها يوسف في (12:77) بالانجليزي

(12:77) At this discovery the brothers remarked, "There is nothing strange in it that he has committed a theft, for his brother (Joseph) also committed a theft before this. " *61 Hearing this, Joseph suppressed his feelings and did not reveal the secret to them, but said only this in an under tone, "What a bad people you are! you are accusing me (to my face) of the thing the truth of which Allah knows best."

Tafseer Abu-al-A'la Maududi

Page 244 English Traditional

*61) As regards the question why it was not worthy of Prophet Joseph to apply the king's law to his personal case, its best answer is again found in the practice of the Holy Prophet. During the interim period, when the laws of ignorance had not yet been replaced by Islamic Laws, other Muslims went on drinking wine and taking interest as before, but the Holy Prophet never practiced any of these things. Likewise some un-Islamic laws of marriage, such as taking in marriage of real sisters at one and the same time, were practised, but the Holy Prophet never practised any such thing. Thus it is clear, that there was a difference between leaving in vogue some un-Islamic laws during the period of the evolution of the Islamic Law and practising the same. Had Prophet Joseph applied the king's law to his own case, it would have meant that he had lent his seeming sanction to that law. But it is obvious that a Prophet, who is sent to eliminate the ways of ignorance. cannot follow these even under the temporary leave that is given to others.
Their position and dissociated themselves from Benjamin, declaring that he was a thief like his brother Joseph. It is obvious that this was a false accusation the clever brothers had invented on the spot. But it is an instance of the malice these brothers bore to their two step-brothers, and is also the answer to the question why Prophet Joseph desired to keep his brother with him.