How can I apply a rule, so only Backlog Items can change from status when they are connected to a Sprint?

[Bas Heemskerk]

I want to Apply a rule for changing the status from an Item, it has to be connected to a Sprint to go from "To Do" to the next status.

[Nic Brough -Adaptavist-]

The best way to do this is to add a "validator" to the workflow transition from To-do to the next status.  A simple "sprint is not empty" one will do it.  (You could also do it with a "condition", but that would hide the transition from people and there's no way to tell them on-screen what is missing.  A validator will tell them that the sprint is missing)