لَا تَحْكُمْ عَلَى الْخَبَرِ مُتَعَجِّلًا. فَإِنَّ التَّثَبُّتَ وَاجِبٌ.
Do not judge the report hastily, for verification is necessary.
The second clause provides a reason (taʿlīl) for the instruction; “fa-inna” makes that connection explicit. If the passage instead read “Do not judge hastily. Verification is necessary,” the second independent clause might answer the implied question “Why not?” and so operate as explanatory resumption.
Not every causal explanation should automatically be labeled istiʾnāf, nor every resumption an explicit causal construction. “Reason” describes the semantic relation; “resumption” describes how a clause follows an implied question in discourse. In an appropriate context both analyses may illuminate different aspects of one expression.