Is there a variant rule that you can only use a focus for spells you've cast before?

[Puh Laden]

Is there a (non-homebrew) variant rule that you can only use a spellcasting focus for spells that require material components if you've cast the spell before? My DM thinks it's in the PHB or DMG but I've looked up everything in the PHB on casting and found nothing, and I can't find anything on spellcasting foci in the index to the DMG. If not, might he have gotten the idea from a previous edition?

[Addaran]

So basically... you can't cast Web with a focus if it's the first time. But if you cast it once using some spiderweb, then you're good to use the focus forever?

First time i hear that. But theoretically, it would just be a 25GP taxes (spell component pouch for the first casting) unless your DM also rule that you need every specific component. Might just be a bit annoying when you get new spells, to make sure you find the component.

[Puh Laden]

So basically... you can't cast Web with a focus if it's the first time. But if you cast it once using some spiderweb, then you're good to use the focus forever?

First time i hear that. But theoretically, it would just be a 25GP taxes (spell component pouch for the first casting) unless your DM also rule that you need every specific component. Might just be a bit annoying when you get new spells, to make sure you find the component.

Right, and in the session he brought it up we happened to be in a town with very cheap component pouches, so me and another caster bought some (for me it was just in case the DM didn't change his mind when I let him know it's not actually in a book). It didn't stop me from casting fireball and levitate on level up with only an arcane focus though.