Abu Hurairah reported the Messenger of Allah (ﷺ) as saying: If anyone says a rak'ah of the 'Asr prayer before sunset, he has observed (the 'Asr prayer), and if anyone performs a rak'ah of the Fajr prayer, he has observed (the Fajr prayer)
SahihSahihSahihBook 2 · Hadith 22