In a recent campaign my tiefling took damage from an attack which also knocked them prone. In that case I wanted to use my hellish rebuke as a reaction after being attacked/knocked prone but was told by the DM that I couldn't because I was prone. I was under the impression that one could still cast spells while prone at a disadvantage - but I assumed the reaction/execution order was the reason why I wouldn't be able to hellish rebuke there. Should I have been able to hellish rebuke?
In a recent campaign my tiefling took damage from an attack which also knocked them prone. In that case I wanted to use my hellish rebuke as a reaction after being attacked/knocked prone but was told by the DM that I couldn't because I was prone. I was under the impression that one could still cast spells while prone at a disadvantage - but I assumed the reaction/execution order was the reason why I wouldn't be able to hellish rebuke there. Should I have been able to hellish rebuke?
Being Prone does not hinder you casting spells. This is what the condition says.
Prone
A prone creature's only movement option is to crawl, unless it stands up and thereby ends the condition.
In a recent campaign my tiefling took damage from an attack which also knocked them prone. In that case I wanted to use my hellish rebuke as a reaction after being attacked/knocked prone but was told by the DM that I couldn't because I was prone. I was under the impression that one could still cast spells while prone at a disadvantage - but I assumed the reaction/execution order was the reason why I wouldn't be able to hellish rebuke there. Should I have been able to hellish rebuke?
Being Prone does not hinder you casting spells. This is what the condition says.
And as Hellish Rebuke is a spell that forces a saving throw it would be unaffected by being prone.
Do remember that it you need to be damaged by a creature and you need to see that creature to be able to cast that spell.