Musnad Abu Ya'la al-Mawsili 115:65

Musa narrated to us, Abd al-Rahman narrated to us, from Jarir ibn Hazim, from Qatadah, who said: I asked Anas ibn Malik, "How was the recitation of the Messenger of Allah (may Allah bless him and grant him peace)?" He said, "He used to extend his voice with an extension."