Sunan an-Nasai Book 18, Hadith 1534

أَخْبَرَنِي عَمْرُو بْنُ عُثْمَانَ بْنِ سَعِيدِ بْنِ كَثِيرٍ، عَنْ مُحَمَّدٍ، عَنِ الزُّبَيْدِيِّ، عَنِ الزُّهْرِيِّ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ بْنِ عُتْبَةَ، أَنَّ عَبْدَ اللَّهِ بْنَ عَبَّاسٍ، قَالَ قَامَ رَسُولُ اللَّهِ صلى الله عليه وسلم وَقَامَ النَّاسُ مَعَهُ فَكَبَّرَ وَكَبَّرُوا ثُمَّ رَكَعَ وَرَكَعَ أُنَاسٌ مِنْهُمْ ثُمَّ سَجَدَ وَسَجَدُوا ثُمَّ قَامَ إِلَى الرَّكْعَةِ الثَّانِيَةِ فَتَأَخَّرَ الَّذِينَ سَجَدُوا مَعَهُ وَحَرَسُوا إِخْوَانَهُمْ وَأَتَتِ الطَّائِفَةُ الأُخْرَى فَرَكَعُوا مَعَ النَّبِيِّ صلى الله عليه وسلم وَسَجَدُوا وَالنَّاسُ كُلُّهُمْ فِي صَلاَةٍ يُكَبِّرُونَ وَلَكِنْ يَحْرُسُ بَعْضُهُمْ بَعْضًا ‏.‏

It was narrated from 'Ubaidullah bin Abdullah bin Utbah that:'Abdullah bin 'Abbas said: "The Messenger of Allah (ﷺ) stood and the people stood with him, and he said the takbir and they said the takbir. Then he bowed, and some of them bowed, then he prostrated and they prostrated, then he stood for the second rak'ah and those who had prostrated with him moved back and guarded their brothers, and the other group came and bowed and prostrated with the Prophet (ﷺ). All the people were praying and saying the takbir, but they were guarding one another