لأن الوجوب غيب عنا، فلابد من علامة يعرف بها وجوب الحكم
Obligation is not directly visible to us; it therefore requires an identifiable sign.
A legal duty cannot simply be observed in a physical event. The law associates it with ascertainable matters: prayer with its time, Ramadan fasting with witnessing the month, and zakat with the requisite property.
A sabab is not an independent legislator or an inherent physical force creating the duty. It is the legally assigned basis by which the obligation can be identified and attributed. The legislative source remains the divine command.