Sahih al-Bukhari 580
Sahih al-Bukhari · Book 9: Times of the Prayers · Whoever got (or was able to offer) one Rak'a of a prayer (in time)
Narrated Abu Huraira:
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ ، قَالَ أَخْبَرَنَا مَالِكٌ ، 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 فَقَدْ أَدْرَكَ الصَّلاَةَ " .
Allah's Messenger (ﷺ) said, "Whoever could get one rak`a of a prayer, (in its proper time) he has got the prayer."