ENOfficial
Abu Huraira reported God’s Messenger as saying, “If anyone performs a rak'a of the Morning Prayer before sunrise, he has observed the Morning Prayer; and if anyone performs a rak'a of the afternoon prayer before sunset, he has observed the afternoon prayer.” (Bukhari and Muslim.)
Source: sunnah.com
Other translations
Arabic
وَعَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «مَنْ أَدْرَكَ رَكْعَةً مِنَ الصُّبْحِ قَبْلَ أَنْ تَطْلُعَ الشَّمْسُ فَقَدْ أَدْرَكَ الصُّبْحَ. وَمَنْ أَدْرَكَ رَكْعَةً مِنَ الْعَصْرِ قَبْلَ أَنْ تغرب الشَّمْس فقد أدْرك الْعَصْر»
sunnah.com