Solve The Rebus Puzzle!

Riddle: Jennifer is always late for work. One day, she comes to work late as usual, which angers her boss. But, her boss is more lenient today and gives Jennifer a chance to keep her job. If she solves his rebus puzzle, Jennifer won't be fired. The boss says, "I'm A B C D E F G H I J K L M N O P Q R S T V W X Y Z!". Luckily, Jennifer was a smart girl and managed to keep her job. What did the rebus puzzle say?