Final answer:
Antonio Salieri was the composer who was jealous of Mozart, but there is no concrete evidence of what he said to Mozart.
Step-by-step explanation:
The composer who was jealous of Mozart was Antonio Salieri. Salieri was a prominent composer during Mozart's time, and he is believed to have harbored jealousy towards Mozart due to his immense talent and popularity. While there is no concrete evidence of what Salieri said to Mozart, it is widely speculated that he made comments expressing his envy and frustrations.