Surah 12. Yusuf, Ayah 66

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.

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.