Abu Dawud Book 2, Hadith Number 1408.
Chapter : If a person listens to a verse in which a prostration occurs and he is riding the beast what should he do.
Narated By Abdullah ibn Umar : The Apostle of Allah (PBUH) used to recite the Qur’an to us. When he came upon the verse containing prostration, he would utter the takbir (Allah is most great) and we would prostrate ourselves along with him.
The narrator ‘Abd al-Razzaq said: Al-Thawri liked this tradition very much.
Abu Dawud said: This was liked by him for this contains the uttering of takbir