(2) Prayer (Kitab Al-Salat)
كتاب الصلاة
(349) Chapter: Those Who Said He Should Complete (The Prayers) Based Upon His Strongest Judgement
(200) باب مَنْ قَالَ يُتِمُّ عَلَى أَكْبَرِ ظَنِّهِ
Sunan Abi Dawud 1031 
This tradition has also been transmitted by Muhammad b. Muslim through a different chain of narrators. This version adds; “While he is sitting before he gives the salutation.”
حَدَّثَنَا حَجَّاجُ بْنُ أَبِي يَعْقُوبَ، حَدَّثَنَا يَعْقُوبُ، حَدَّثَنَا ابْنُ أَخِي الزُّهْرِيِّ، عَنْ مُحَمَّدِ بْنِ مُسْلِمٍ، بِهَذَا الْحَدِيثِ بِإِسْنَادِهِ زَادَ ‏ "‏ وَهُوَ جَالِسٌ قَبْلَ التَّسْلِيمِ ‏"‏ ‏.‏
Grade :  Hasan Sahih (Al-Albani) حسن صحيح  (الألباني)حكم :
Reference : Sunan Abi Dawud 1031
In-book reference : Book 2, Hadith 642
English translation : Book 2, Hadith 1026