Why can “wa-l-ṣidqu aṣlu al-ʿilm” function as tadhyīl after a particular report?

Supplementary Practice 16: Observing the Sky, Evidential Scope and Rhetorical Precision

• It reinforces a particular report through a general principle
• It is a single-word adjective
• It is a cognate object
• It merely adds a time specification