Sunan an-Nasa'i, Book 11, Hadith 90 (In-Book) ⓘ
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). "
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى، قَالَ حَدَّثَنَا قُرَّةُ بْنُ خَالِدٍ، عَنْ مُحَمَّدِ بْنِ سِيرِينَ، عَنْ أَبِي هُرَيْرَةَ، قَالَ سَجَدَ أَبُو بَكْرٍ وَعُمَرُ - رضى الله عنهما - فِي { إِذَا السَّمَاءُ انْشَقَّتْ } وَمَنْ هُوَ خَيْرٌ مِنْهُمَا .
also referenced under: Hadith 965 (Reference) & Volume 2, Book 11, Hadith 966 (DarusSalam)