"Whoever catches up with a Rak'ah of Fajr before the sun rises, then he has caught up with it; and whoever catches up with a Rak'ah of 'Asr before the sun sets, then he has caught up with it." (Using translation from Nasāʾī 551)  

عَنِ النَّبِيِّ ﷺ قَالَ «مَنْ أَدْرَكَ رَكْعَةً مِنَ الْفَجْرِ قَبْلَ أَنْ تَطْلُعَ الشَّمْسُ فَقَدْ أَدْرَكَهَا وَمَنْ أَدْرَكَ رَكْعَةً مِنَ الْعَصْرِ قَبْلَ أَنْ تَغْرُبَ الشَّمْسُ فَقَدْ أَدْرَكَهَا»  

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). (Using translation from Abū Dāʾūd 412)   

أَنَّ رَسُولَ اللهِ ﷺ قَالَ «مَنْ أَدْرَكَ مِنْ صَلَاةِ الصُّبْحِ رَكْعَةً قَبْلَ أَنْ يَطْلُعَ قَرْنُ الشَّمْسِ الْأَوَّلِ فَقَدْ أَدْرَكَ وَمَنْ أَدْرَكَ مِنْ صَلَاةِ الْعَصْرِ رَكْعَةً أَوِ ثِنْتَيْنِ قَبْلَ أَنْ تَغْرُبَ الشَّمْسُ فَقَدْ أَدْرَكَ»  

"Whoever catches up with a prostration of Subh before the sun rises, then he has caught up with it; and whoever catches up with a prostration of 'Asr before the sun sets, then he has caught up with it." (Using translation from Nasāʾī 550)  

عَنِ النَّبِيِّ ﷺ قَالَ «مَنْ أَدْرَكَ سَجْدَةً مِنَ الصُّبْحِ قَبْلَ أَنْ تَطْلُعَ الشَّمْسُ فَقَدْ أَدْرَكَهَا وَمَنْ أَدْرَكَ سَجْدَةً مِنَ الْعَصْرِ قَبْلَ أَنْ تَغْرُبَ الشَّمْسُ فَقَدْ أَدْرَكَهَا»