11. The Book of the Commencement of the Prayer - كتاب الافتتاح
51) Chapter: The Prostration in: "When the heaven is split asunder"
It was narrated that Abu Hurairah said:
"Abu Bakr and Umar prostrated during: 'When the heaven is split asunder,' as did the one who was better than them (the Prophet (ﷺ)). "