Translation:

66. (Jacob) said: "Never will I send him with you until ye swear a solemn oath to me in Allah's name that ye will be sure to bring him back to me unless ye are yourselves hemmed in (and made powerless)." And when they had sworn their solemn oath he said: "Over all that we say be Allah the Witness and Guardian!"

Notes (Tafseer)

1728. The appeal to the family's needs in the time of famine at length made Jacob relent, but he exacted a solemn promise from the brothers, under the most religious sanctions, that they would bring Benjamin back to him, unless they were themselves prevented, as the Insurance Policies say "by an act of God," so that they became really powerless. To that promise Jacob called Allah to witness.

1729. This is more than a formula. Allah is invoked as present and witnessing the bargain, and to Him both parties make over the affair to arrange and fulfil.