Maliks Muwatta Book 3, Hadith Number 44.
Section : Reciting to Oneself behind the Imam when He does not Recite Aloud.
Yahya related to me from Malik from Yazid ibn Ruman that Nafi ibn Jubayr ibn Mutim used to recite behind the imam when he did not recite aloud.
Malik said, “That is the most preferable to me of what I have heard about the matter.”