Sahih Al Bukhari Hadith Number 1075

Narrated Ibn `Umar: When the Prophet (peace be upon him) recited a Sura that contained the prostration he would prostrate and we would do the same and some of us (because of the heavy rush) could not find a place for prostration.

17  Prostration During Recital of Qur’an
Hadith number 1075
Volume no 2
Chapter: 8 (Whoever prostrated with the prostration of the reciter)