Your cough subsides when you take that tasty grape flavored cough syrup. you always take the syrup when you have a cough, because it works. this is an example of

negative reinforcement

Explanation: Negative reinforcement occurs when a certain stimulus is removed after a type of behavior is exhibited. The likelihood of the particular behavior occurring again in the future is increased because of removing/avoiding the negative consequence.

Muhammad was the founder/leader and when he died, there were a lot of issues about who would the new leader. The group split into the Sunni who wanted to elect their new leader and the Shia who thought it should be someone in Muhammad's family.