(17) باب مَنْ أَدْرَكَ رَكْعَةً مِنَ الْعَصْرِ قَبْلَ الْغُرُوبِ
Narrated Abu Huraira:
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."
Reference: Sahih al-Bukhari 556
In-book reference: Book 9, Hadith 33
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 10, Hadith 531