The two prayers that are hardest to keep
Whoever manages the one before sunrise and the one before sunset will not enter the Fire.
أَمَا إِنَّكُمْ سَتَرَوْنَ رَبَّكُمْ كَمَا تَرَوْنَ هَذَا، لاَ تُضَامُّونَ ـ أَوْ لاَ تُضَاهُونَ ـ فِي رُؤْيَتِهِ، فَإِنِ اسْتَطَعْتُمْ أَنْ لاَ تُغْلَبُوا عَلَى صَلاَةٍ قَبْلَ طُلُوعِ الشَّمْسِ، وَقَبْلَ غُرُوبِهَا فَافْعَلُوا
Whoever prays before the rising of the sun and before its setting will not enter the Fire.
Fajr and ʿAsr: the one that costs you sleep and the one that lands in the middle of work.
The full narration
Narrated Jarir bin `Abdullah:We were with the Prophet (ﷺ) on a full moon night. He looked at the moon and said, "You will certainly see your Lord as you see this moon, and there will be no trouble in seeing Him. So if you can avoid missing (through sleep, business, etc.) a prayer before the rising of the sun (Fajr) and before its setting (`Asr) you must do so. He (the Prophet (ﷺ) ) then recited the following verse: And celebrate the praises Of Your Lord before The rising of the sun And before (its) setting
Source
Ṣaḥīḥ al-Bukhārī · 573
- Agreed upon as authentic (al-Bukhārī / Muslim)