والعلم الثابت به أي بخبر الرسول يضاهي أي يشابه العلم الثابت بالضرورة
Knowledge established through the messenger's report resembles necessary knowledge in its certainty.
Necessary and inferential describe different modes of acquisition; the latter does not necessarily mean probable or weak. A conclusion reached from certain premises by valid inference may itself be certain.
A mathematical result may need several steps of proof while remaining fully certain when demonstrated. Likewise, once a prophetic mission and the transmission of a report are securely established, the content of the report is accepted as certain within this framework.