أَخْبَرَنَا مَحْمُودُ بْنُ غَيْلاَنَ، قَالَ حَدَّثَنِي أَبُو دَاوُدَ، قَالَ أَنْبَأَنَا شُعْبَةُ، عَنْ مُوسَى بْنِ أَبِي عَائِشَةَ، قَالَ سَمِعْتُ عُبَيْدَ اللَّهِ بْنَ عَبْدِ اللَّهِ، يُحَدِّثُ عَنْ عَائِشَةَ، رضى الله عنها أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم أَمَرَ أَبَا بَكْرٍ أَنْ يُصَلِّيَ بِالنَّاسِ قَالَتْ وَكَانَ النَّبِيُّ صلى الله عليه وسلم بَيْنَ يَدَىْ أَبِي بَكْرٍ فَصَلَّى قَاعِدًا وَأَبُو بَكْرٍ يُصَلِّي بِالنَّاسِ وَالنَّاسُ خَلْفَ أَبِي بَكْرٍ ‏.‏

It was narrated from Aisha may Allah be pleased with her, that the Messenger of Allah (PBUH) told Abu Bakr to lead the people in prayer. She said: "The Prophet was in front of Abu Bakr and he prayed sitting down, and Abu Bakr was leading the people in prayer, and the people were behind Abu Bakr." Translation Not Available

Book Ref: Sunan An Nisai Book 10 Hadith 797
Web Ref:  Sunan An Nisai Vol 1 Book 10 Hadith 798