(2) Prayer (Kitab Al-Salat)
كتاب الصلاة
(219) Chapter: About The Imam Praying While Sitting Down
(69) باب الإِمَامِ يُصَلِّي مِنْ قُعُودٍ
Sunan Abi Dawud 606 
Jabir said :
when the prophet (ﷺ) became seriously ill, we prayed behind him while he was sitting and Abu Bakr was calling “Allah is most great “ to cause the people to hear the TAKBIR. Then he (the narrators) narrated the rest of the tradition.
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، وَيَزِيدُ بْنُ خَالِدِ بْنِ مَوْهَبٍ، - الْمَعْنَى - أَنَّ اللَّيْثَ، حَدَّثَهُمْ عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، قَالَ اشْتَكَى النَّبِيُّ صلى الله عليه وسلم فَصَلَّيْنَا وَرَاءَهُ وَهُوَ قَاعِدٌ وَأَبُو بَكْرٍ يُكَبِّرُ لِيُسْمِعَ النَّاسَ تَكْبِيرَهُ ثُمَّ سَاقَ الْحَدِيثَ ‏.‏
Grade :  Sahih (Al-Albani) صحيح  (الألباني)حكم :
Reference : Sunan Abi Dawud 606
In-book reference : Book 2, Hadith 216
English translation : Book 2, Hadith 606