If you’re in a country that uses references, it’s best to request an interim report from your current employer, then use this to apply for a new job and finally, when you signed the new contract, quit the old job. The reason is: That way your employer is interested in writing a positive, truthful reference to not anger you. When you have already quit or are beeing fired, they may have negative feelings about you or may want to force you back by making you look as unemployable as possible.