BACKGROUND: I played a Saga Rite of Belzenlok. When the saga fully resolves you end up with four 0/1 Cleric creature tokens and a 6/6 black Demon creature with flying and trample. At the beginning of my next upkeep I have to sacrifice a creature or the Demon token creature deals 6 damage to me. “At the beginning of your upkeep, sacrifice another creature. If you can’t, this creature deals 6 damage to you.”
At the beginning of my up keep I specified that I was sacrificing one of the 0/1 Cleric token creatures. My opponent played an instant spell (Shock) killing the 0/1 Cleric token. He then claimed that I revived 6 damage from the token Demon since I did not sacrifice a creature.
QUESTION: Can an Instant spell be played during upkeep to interrupt a triggered ability?
If so, in the situation described above, do I receive the 6 damage as my opponent claims?