Sahih al-Bukhari 556
Sahih al-Bukhari · Book 9: Times of the Prayers · Whoever got (or was able to offer) only one Rak'a of the 'Asr prayer before sunset
Narrated Abu Huraira:
حَدَّثَنَا أَبُو نُعَيْمٍ ، قَالَ حَدَّثَنَا شَيْبَانُ ، عَنْ يَحْيَى ، عَنْ أَبِي سَلَمَةَ ، عَنْ أَبِي هُرَيْرَةَ ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِذَا أَدْرَكَ أَحَدُكُمْ سَجْدَةً مِنْ صَلاَةِ الْعَصْرِ قَبْلَ أَنْ تَغْرُبَ الشَّمْسُ فَلْيُتِمَّ صَلاَتَهُ، وَإِذَا أَدْرَكَ سَجْدَةً مِنْ صَلاَةِ الصُّبْحِ قَبْلَ أَنْ تَطْلُعَ الشَّمْسُ فَلْيُتِمَّ صَلاَتَهُ " .
Allah's Messenger (ﷺ) said, "If anyone of you can get one rak`a of the `Asr prayer before sunset, he should complete his prayer. If any of you can get one rak`a of the Fajr prayer before sunrise, he should complete his prayer."