Ancient conquering kings cut a strip from each defeated king's robe and sewed it onto their own train, so a king's train length recorded how many rivals he'd beaten, which is what Isaiah 6:1's 'train of his robe filled the temple' is trading on.

Isaiah 6:1 itself is solid ground: a king's long train (the Hebrew word shul also covers "hem" and "skirt") was a genuine ancient status marker. The more important a person was, the longer and more elaborate their train, because being slowed down by trailing fabric was itself a display of not having to work; Egyptian and Assyrian royal dress shows the same idea. "His train filled the temple" as a picture of unbounded majesty needs no extra background story to land.

What doesn't hold up is the specific, widely-preached claim that kings tallied conquests by literally cutting a piece of cloth from each defeated rival's robe and stitching it onto their own train. A wide search (ancient Near Eastern inscriptions and reliefs, historical scholarship on Persian, Ottoman, and European robe customs, and a large theological reference library) turns up no source describing this practice, in any period or region. What the sources do describe points the opposite direction: cutting or grabbing someone's hem was a real symbolic act in the ancient world, but it signaled dissolving an alliance or stripping someone of authority (Samuel tearing Saul's hem, David cutting Saul's robe), while attaching one person's hem to another's sealed a covenant or marriage bond: a story about connection, not a conquest scoreboard.

Tracing the claim itself: the earliest instance findable anywhere is a December 2007 blog post where the author describes it as a personal impression from a church service, not researched history. It then circulated, nearly word for word, across sermon blogs and devotionals for over a decade, and gained an appearance of scholarly weight in 2014 when it turned up in a self-published commentary with no citation at all. This is worth publishing as a genuinely open case rather than a clean debunk: the search for supporting evidence has been about as thorough as it can get, but it can't rule out an oral tradition older than 2007 that was simply never written down. What can be said plainly is that if you've heard this preached as documented ancient history, it isn't. It's a preacher's illustration less than twenty years old, and Isaiah's own point about God's limitless majesty doesn't need it to stand.