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" (Using translation from Abū Dāʾūd 1407)  

«سَجَدْنَا مَعَ رَسُولِ اللَّهِ ﷺ فِي إِذَا السَّمَاءُ انْشَقَّتْ وَاقْرَأْ بِاسْمِ رَبِّكَ»