Sunan Abi Dawud, Hadith 1121 ⓘ
Abu Hurairah reported the Messenger of Allah as saying: If anyone obtains a rak'ah in the prayer (along with the imam), he has obtained the whole prayer.
حَدَّثَنَا الْقَعْنَبِيُّ، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ أَدْرَكَ رَكْعَةً مِنَ الصَّلاَةِ فَقَدْ أَدْرَكَ الصَّلاَةَ " .
also referenced under: Hadith 1116 (Hasan) & Book 3, Hadith 1116 (USC-MSA)