Abu Dawud said; This tradition has been narrated in a similar manner by Ibn "Uyainab, Ma'mar and al-Laith.
In-book : Book 2, Hadith 641
English translation : Book 2, Hadith 1025
2. Prayer (Kitab Al-Salat)
باب مَنْ قَالَ يُتِمُّ عَلَى أَكْبَرِ ظَنِّهِ