Spell-Like Abilities don’t need material components to function. However, Soul Bind specifically requires a gem with a certain value corresponding to the target’s HD for the soul to be trapped in. So how does that work out? Does the gem appear out of nowhere?
The answer:
It seems to depend. Night hags trap souls within their Heartstone, but for other casters (such as for the Pit Fiend), it would make sense for the soul to crystallize and become the gem itself.