Gandalf Vs. The Witch King

First of all apologies for double posting, it is necessary as this is a separate point.

Somebody posted a long time ago about the fact that the Lord of the Nazgul was shaken by the fire of Gandalf at Weathertop, & that he also narrowly missed being pierced by a deadly blade, Sting, wielded by Frodo which would have been more lethal to him than the wound suffered by Frodo at the hands of the Morgul knife. I would very much like to know where this extract came from, since it also suggests that in the aftermath the Witch King was left reeling & even afraid of both Gandalf & Frodo.