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

In verse 78, it was said: قَالُوا يَا أَيُّهَا الْعَزِيزُ إِنَّ لَهُ أَبًا شَيْخًا كَبِيرً‌ا فَخُذْ أَحَدَنَا مَكَانَهُ ۖ إِنَّا نَرَ‌اكَ مِنَ الْمُحْسِنِين . It means when the brothers of Sayyidna Yusuf (علیہ السلام) realized that nothing seems to be working here and they have no option left but to leave Benyamin behind, they started flattering the ` Aziz of Misr. They told him that Benyamin's father was very old and weak (his separation will be unbearable for him). Therefore, they requested him that he should detain anyone from among them, in lieu of him. They also told him that they were making that request to him in the hope that he, as they feel, appears to be a very generous person - or, he has been gener-ous to them earlier too.