Narrated Anas bin Malik:

While the Muslims were offering the Fajr prayer on Monday and Abu Bakr was leading them in prayer, suddenly Allah's Apostle lifted the curtain of 'Aisha's dwelling and looked at them while they were in the rows of the prayers and smiled. Abu Bakr retreated to join the row, thinking that Allah's Apostle wanted to come out for the prayer. The Muslims were about to be put to trial in their prayer (i.e. were about to give up praying) because of being overjoyed at seeing Allah's Apostle. But Allah's Apostle beckoned them with his hand to complete their prayer and then entered the dwelling and let fall the curtain.

حَدَّثَنَا سَعِيدُ بْنُ عُفَيْرٍ، قَالَ حَدَّثَنِي اللَّيْثُ، قَالَ حَدَّثَنِي عُقَيْلٌ، عَنِ ابْنِ شِهَابٍ، قَالَ حَدَّثَنِي أَنَسُ بْنُ مَالِكٍ ـ رضى الله عنه ـ أَنَّ الْمُسْلِمِينَ، بَيْنَا هُمْ فِي صَلاَةِ الْفَجْرِ مِنْ يَوْمِ الاِثْنَيْنِ وَأَبُو بَكْرٍ يُصَلِّي لَهُمْ لَمْ يَفْجَأْهُمْ إِلاَّ رَسُولُ اللَّهِ ﷺ قَدْ كَشَفَ سِتْرَ حُجْرَةِ عَائِشَةَ، فَنَظَرَ إِلَيْهِمْ وَهُمْ فِي صُفُوفِ الصَّلاَةِ. ثُمَّ تَبَسَّمَ يَضْحَكُ، فَنَكَصَ أَبُو بَكْرٍ عَلَى عَقِبَيْهِ لِيَصِلَ الصَّفَّ، وَظَنَّ أَنَّ رَسُولَ اللَّهِ ﷺ يُرِيدُ أَنْ يَخْرُجَ إِلَى الصَّلاَةِ فَقَالَ أَنَسٌ وَهَمَّ الْمُسْلِمُونَ أَنْ يَفْتَتِنُوا فِي صَلاَتِهِمْ فَرَحًا بِرَسُولِ اللَّهِ ﷺ فَأَشَارَ إِلَيْهِمْ بِيَدِهِ رَسُولُ اللَّهِ ﷺ أَنْ أَتِمُّوا صَلاَتَكُمْ، ثُمَّ دَخَلَ الْحُجْرَةَ وَأَرْخَى السِّتْرَ.