We prostrated ourselves along with the Messenger of Allah ﷺ on account of: "When the sky is rent asunder" and "Recite in the name of Your Lord Who created"  

سَجَدْنَا مَعَ رَسُولِ اللَّهِ ﷺ فِي { إِذَا السَّمَاءُ انْشَقَّتْ } وَ { اقْرَأْ بِاسْمِ رَبِّكَ الَّذِي خَلَقَ }  

I offered the night prayer behind Abu Hurairah. He recited Surah Inshiqaq ("When the sky is rent asunder") and prostrated himself. I asked him: What is this prostration ? He replied: I prostrated myself on account of this (surah) behind Abu al-Qasim (i.e. the Prophet). I shall continue prostrating on account of this till I meet him.  

صَلَّيْتُ مَعَ أَبِي هُرَيْرَةَ الْعَتَمَةَ فَقَرَأَ { إِذَا السَّمَاءُ انْشَقَّتْ } فَسَجَدَ فَقُلْتُ مَا هَذِهِ السَّجْدَةُ قَالَ سَجَدْتُ بِهَا خَلْفَ أَبِي الْقَاسِمِ ﷺ فَلاَ أَزَالُ أَسْجُدُ بِهَا حَتَّى أَلْقَاهُ