فدين الله أحق
A duty owed to Allah has an even stronger claim to be discharged.
The comparison does not merely join the labels 'debt' and 'pilgrimage'. Its focus is the legally recognized possibility of performing an obligation in a way that benefits the person responsible, where substitution is allowed.
Worked analysis:
Original: paying another person's debt.
New case: performing pilgrimage on another's behalf.
Relevant connection: legally recognized fulfillment of another's obligation.
Conclusion: permission for substitution under the conditions stated for pilgrimage.
Irrelevant attributes, such as a debt's being financial, are not mechanically transferred into every rule governing pilgrimage.