Is the hadith, "I have left among you two admonishers, one speaking and one silent: the speaking one is the Qur'an and the silent one is death," an authentic hadith from the Messenger of Allah, peace and blessings be upon him?

The aforementioned hadith was not reported, but it was stated in Imam Malik's Muwatta' that the Messenger of Allah, may Allah's prayers and peace be upon him, said: "I have left among you two things, which if you hold fast to them, you will never go astray: the Book of Allah and the Sunnah of His Prophet." And it was narrated from him, may Allah's prayers and peace be upon him, that he used to say: "Death is sufficient as a preacher, certainty is sufficient as richness, and worship is sufficient as an occupation." And it was authentically reported from him, may Allah's prayers and peace be upon him, that he said: "Increase in remembering the destroyer of pleasures," meaning death.