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."
Sahih al-Bukhari Book 9, Hadith 33
← Previous Hadith Allah's Messenger (ﷺ) said, "Angels come to you in succession by night and day and all of them get together at the time of the Fajr and `Asr prayers. Those who have passed the night with you (or stayed with you) ascend (to the Heaven) and Allah asks them, though He knows everything about you, well, "In what state did you leave my slaves?" The angels reply: "When we left them they were praying and when we reached them, they were praying."

Sahih al-Bukhari Book 9, Hadith 32 Next Hadith → My father said, "I heard Allah's Messenger (ﷺ) saying, 'The period of your stay as compared to the previous nations is like the period equal to the time between the `Asr prayer and sunset. The people of the Torah were given the Torah and they acted (upon it) till midday then they were exhausted and were given one Qirat (of gold) each. And then the people of the Gospel were given the Gospel and they acted (upon it) till the `Asr prayer then they were exhausted and were! given one Qirat each. And then we were given the Quran and we acted (upon it) till sunset and we were given two Qirats each. On that the people of both the scriptures said, 'O our Lord! You have given them two Qirats and given us one Qirat, though we have worked more than they.' Allah said, 'Have I usurped some of your right?' They said, 'No.' Allah said: "That is my blessing I bestow upon whomsoever I wish."

Sahih al-Bukhari Book 9, Hadith 34