Sunan an-Nasa'i 965
سنن النسائي#965SahihIt 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)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 11:90