«تَتَبُّعُ الطُّرُقِ ... لِيُعْلَمَ هَلْ لَهُ مُتَابِعٌ أَمْ لَا»
Tracing the routes to discover whether a supporting transmitter exists.
I‘tibar is the systematic search for, and comparison of, a report's transmission paths. That investigation may reveal a mutabi‘, a shahid from another Companion, or no sufficiently relevant corroborating path.
It is not a third species of supporting narration parallel to mutaba‘ah and shahid. It is the method of investigation through which such routes may be found.