Three terms structure an acknowledgment:
Muqirr is the person admitting the right.
Muqarr lahu is the beneficiary of that admission.
Muqarr bihi is the admitted right or property.
If Bakr says he holds Khalid's book on trust, Bakr is the acknowledging party, Khalid the beneficiary, and the book the subject. An unspecified right is not the same as an unspecified rights-holder.
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Three elements of an admission
Kitab al-Iqrar: Capacity, Unspecified Rights, and Amounts in Admissions
Three terms structure an acknowledgment:
Muqirr is the person admitting the right.
Muqarr lahu is the beneficiary of that admission.
Muqarr bihi is the admitted right or property.
If Bakr says he holds Khalid's book on trust, Bakr is the acknowledging party, Khalid the beneficiary, and the book the subject. An unspecified right is not the same as an unspecified rights-holder.