You are reading a tafsir for the group of verses 12:78 to 12:79

Yusuf's Brothers offer taking One of Them instead of Binyamin as a Slave, Yusuf rejects the Offer

When it was decided that Benyamin was to be taken and kept with Yusuf according to the law they adhered by, Yusuf's brothers started requesting clemency and raising compassion in his heart for them,

قَالُواْ يأَيُّهَا الْعَزِيزُ إِنَّ لَهُ أَبًا شَيْخًا كَبِيرًا

(They said, "O `Aziz! Verily, he has an old father...") who loves him very much and is comfor- ted by his presence from the son that he lost,

فَخُذْ أَحَدَنَا مَكَانَهُ

(so take one of us in his place.), instead of Binyamin to remain with you,

إِنَّا نَرَاكَ مِنَ الْمُحْسِنِينَ

(Indeed we think that you are one of the doers of good.), the good doers, just, and accepting fairness,

قَالَ مَعَاذَ اللَّهِ أَن نَّأْخُذَ إِلاَّ مَن وَجَدْنَا مَتَـعَنَا عِندَهُ

(He said: "Allah forbid, that we should take anyone but him with whom we found our property..."), `according to the judgement that you gave for his punishment,

إِنَّـآ إِذًا لَّظَـلِمُونَ

(Indeed, we should be wrongdoers.), if we take an innocent man instead of the guilty man. '