Maliks Muwatta Book 3, Hadith Number 45.

Section : Not Reciting behind the Imam when He Recites Aloud.

Yahya related to me from Malik from Nafi that Abdullah ibn Umar, when asked if anyone should recite behind an imam, said, “When you pray behind an imam then the recitation of the imam is enough for you and when you pray on your own you must recite.” Nafi added, “Abdullah ibn ‘Umar used not to recite behind the imam.”

Yahya said that he heard Malik say, “The position with us is that aman recites behind the imam when the imam does not recite aloud and he refrains from reciting when the imam recites aloud.”