Can you store a Spell Glyph with a spell scroll of a prepared spell?

Question

This is a follow-up to a previous question of mine (Can you store a Spell Glyph with a spell scroll of a non-prepared spell?) where it was established that you do need to have a spell prepared in order to be able to spell glyph it.

This question is a slight twist to the previous one: if you do have the spell prepared, but also have a spell scroll of the same spell, are you able to make the Spell Glyph by using the spell scroll instead of a spell slot?

Ex: Bob the 5th level Wizard having "Haste" and "Glyph of Warding" prepared, and in possession of a Spell Scroll of Haste, willing to cast a Spell Glyph of Haste, but using the scroll instead of a spell slot, therefore only using a slot and a scroll instead of two slots.

A supporting argument for a "Yes" answer would be that the Glyph of Warding's Spell Glyph section does not mention the mandatory use of a spell slot for the spell to glyph, just that it must be prepared.

You can store a prepared spell of 3rd level or lower in the glyph by casting it as part of creating the glyph.

Answer 1

Sure! But it would destroy the scroll

In a previous answer to another question, it points out that spells cast from magical items and prepared spells are in different categories. However, it's possible to have them in both categories in the same time. You could be able to cast the spell Haste via the Spell Scroll magic item, and you could also have it "prepared".

Glyph of Warding's text states (PHB, p. 246, bold added):

You can store a prepared spell of 3rd level or lower in the glyph by casting it as part of creating the glyph.

So you are required to do two things:

1. Have the spell prepared
2. Cast the spell

But you are not required by the text to cast the spell via your spell slots. As long as it is prepared and you cast it (and it is of the appropriate level), you have satisfied Glyph of Warding's requirements.

It would be a somewhat odd choice to use a Spell Scroll for this undertaking though, since spell slots are a renewable resource while Spell Scrolls are single use resources only. After all, the rules on Spell Scrolls state (DMG, p. 200, bold added):

Once the spell is cast, the words on the scroll fade, and the scroll itself crumbles to dust.

And as has been stated above, you must cast the spell to store it in the Glyph of Warding. As such, the scroll would crumble into dust when you completed your casting of Glyph of Warding (it would not wait until the Glyph actually activated).

But if you find yourself in a situation where this strategy is desirable (such as when you only have one third level spell slot, but also have an hour to cast Glyph of Warding, or if you are casting a spell via an item that uses charges to cast spells and prefer to spend a charge to a slot [thanks to MarkTO for suggesting this]), it should work.

Answer 2

The Glyph of Warding Spell Glyph option notes:

You can store a prepared spell of 3rd or lower level in the glyph by casting it [the prepared spell] as part of casting the glyph...

There are further limitations to the spell to be cast with the glyph, but they are irrelevant to the question.

So it should be established that you are required to have the spell prepared, and must cast it as part of the Spell Glyph. The Spell Glyph never says you must expend a spell slot for the second spell (unlike Contingency, which explicitely states it expends a slot for both Contingency and the contingent spell). As such, using a scroll for the Spell Glyph, while fully possible, is pointless, as it wouldn't even be used up. If you have the spell prepared (a pre-req for Spell Glyph), you cast Glyph of Warding with that spell, but don't expend a spell slot (or scroll) to do so. You're able to use the spell because it's prepared, not because of a spell slot or scroll.

I would say yes, you can have a scroll instead, but you don't need to as you only need the spell prepared. I would probably say you would still need to be able to fill the components (verbal, somatic, and material), and a scroll removes the need for material. So if the spell had an actual material cost, the scroll would be used up rather than the material. But if the spell only needed a material (not consumed or of a gp value), the scroll could remove the need for the material without being used up (as that would only come into play if the caster was missing their component pouch or arcane focus). Of course, the caster still needs the components for the Glyph of Warding spell.