When he( the imam) recites the Qur'an, keep silence(and listen attentively). And in the tashahhud this version adds after the words "I testify that there is no god but Allah" the words "He is alone, and there is no associate of Him."

Abu Dawud said: His word "And keep silence" is not guarded; it has been narrated by Sulaiman al-Taimi alone in his version.