Sahih al-Bukhari 1205
Narrated Anas bin Malik:
While Abu Bakr was leading the people in the morning prayer on a 
     Monday, the Prophet (ﷺ) came towards them suddenly having lifted the 
     curtain of 'Aisha's house, and looked at them as they were standing in
     rows and smiled. Abu Bakr tried to come back thinking that Allah's 
     Apostle wanted to come out for the prayer. The attention of the 
     Muslims was diverted from the prayer because they were delighted to 
     see the Prophet. The Prophet (ﷺ) waved his hand to them to complete their 
     prayer, then he went back into the room and let down the curtain. The 
     Prophet expired on that very day.
حَدَّثَنَا بِشْرُ بْنُ مُحَمَّدٍ، أَخْبَرَنَا عَبْدُ اللَّهِ، قَالَ يُونُسُ قَالَ الزُّهْرِيُّ أَخْبَرَنِي أَنَسُ بْنُ مَالِكٍ، أَنَّ الْمُسْلِمِينَ، بَيْنَا هُمْ فِي الْفَجْرِ يَوْمَ الاِثْنَيْنِ، وَأَبُو بَكْرٍ ـ رضى الله عنه ـ يُصَلِّي بِهِمْ فَفَجَأَهُمُ النَّبِيُّ صلى الله عليه وسلم قَدْ كَشَفَ سِتْرَ حُجْرَةِ عَائِشَةَ ـ رضى الله عنها ـ فَنَظَرَ إِلَيْهِمْ، وَهُمْ صُفُوفٌ، فَتَبَسَّمَ يَضْحَكُ، فَنَكَصَ أَبُو بَكْرٍ ـ رضى الله عنه ـ عَلَى عَقِبَيْهِ، وَظَنَّ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم يُرِيدُ أَنْ يَخْرُجَ إِلَى الصَّلاَةِ، وَهَمَّ الْمُسْلِمُونَ أَنْ يَفْتَتِنُوا فِي صَلاَتِهِمْ فَرَحًا بِالنَّبِيِّ صلى الله عليه وسلم حِينَ رَأَوْهُ، فَأَشَارَ بِيَدِهِ أَنْ أَتِمُّوا، ثُمَّ دَخَلَ الْحُجْرَةَ وَأَرْخَى السِّتْرَ، وَتُوُفِّيَ ذَلِكَ الْيَوْمَ‏.‏