"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."  

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  

"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."  

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