The Book of Mosques and Places of Prayer
5/30. Chapter:
The one who catches up with a rak`ah of the prayer, he has caught up with that prayer
Sahih Muslim
وَحَدَّثَنِي حَرْمَلَةُ بْنُ يَحْيَى، أَخْبَرَنَا ابْنُ وَهْبٍ، أَخْبَرَنِي يُونُسُ، عَنِ ابْنِ شِهَابٍ، عَنْ أَبِي سَلَمَةَ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " مَنْ أَدْرَكَ رَكْعَةً مِنَ الصَّلاَةِ مَعَ الإِمَامِ فَقَدْ أَدْرَكَ الصَّلاَةَ " .
Abu Huraira reported the Messenger of Allah (ﷺ) as saying: He who finds one rak'ah of the prayer with the Imam, he in fact finds the prayer.
Reference : Sahih Muslim 607bIn-book reference : Book 5, Hadith 206USC-MSA web (English) reference : Book 4, Hadith 1261