Sahih al-Bukhari 1079
Sahih al-Bukhari · Book 17: Prostration During Recital of Qur'an · Whoever does not find a place for prostration (with the Imam) because of overcrowding
Narrated Ibn `Umar.:
حَدَّثَنَا صَدَقَةُ ، قَالَ أَخْبَرَنَا يَحْيَى ، عَنْ عُبَيْدِ اللَّهِ ، عَنْ نَافِعٍ ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنهما ـ قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم يَقْرَأُ السُّورَةَ الَّتِي فِيهَا السَّجْدَةُ فَيَسْجُدُ وَنَسْجُدُ حَتَّى مَا يَجِدُ أَحَدُنَا مَكَانًا لِمَوْضِعِ جَبْهَتِهِ.
Whenever the Prophet (ﷺ) recited the Sura which contained the prostration of recitation he used to prostrate and then, we, too, would prostrate and some of us did not find a place for prostration.