The third type has time as its measure, but not as the cause of the obligation. The example is a fast vowed for a named day:
لِلَّهِ عَلَيَّ أَنْ أَصُومَ يَوْمَ الْجُمُعَةِ
“I owe Allah a fast on Friday.”
The two roles are different:
• The vow makes the fast binding: this is its cause.
• The specified day fixes the fast's time and measures its duration.
It is not merely the arrival of a Friday that creates this vowed duty. The person's vow made the named day's fast binding.
- A Fast Vowed for a Particular Day