"When the "Surat-An-Nasr", 'When comes the Help of Allah and the conquest,' had been revealed to the Prophet ﷺ he did not offer any prayer except that he said therein, "Subhanka Rabbana wa bihamdika; Allahumma ighfirli (I testify the Uniqueness of our Lord, and all the praises are for Him: O Allah, forgive me!")  

مَا صَلَّى النَّبِيُّ ﷺ صَلاَةً بَعْدَ أَنْ نَزَلَتْ عَلَيْهِ {إِذَا جَاءَ نَصْرُ اللَّهِ وَالْفَتْحُ} إِلاَّ يَقُولُ فِيهَا سُبْحَانَكَ رَبَّنَا وَبِحَمْدِكَ اللَّهُمَّ اغْفِرْ لِي  

Messenger of Allah ﷺ used to say very often in bowing and prostration (during his prayers), Subhanka Allahumma Rabbana wa bihamdika; Allahumma ighfirli," according to the order of the Qur'an.  

كَانَ رَسُولُ اللَّهِ ﷺ يُكْثِرُ أَنْ يَقُولَ فِي رُكُوعِهِ وَسُجُودِهِ سُبْحَانَكَ اللَّهُمَّ رَبَّنَا وَبِحَمْدِكَ اللَّهُمَّ اغْفِرْ لِي يَتَأَوَّلُ الْقُرْآنَ  

ʿUmar asked the people regarding Allah's Statement: 'When comes the Help of Allah (to you O Muhammad against your enemies) and the conquest of Mecca.' (110.1) They replied, "It indicates the future conquest of towns and palaces (by Muslims)." ʿUmar said, "What do you say about it, O Ibn ʿAbbas?" I replied, "(This Surat) indicates the termination of the life of Muhammad. Through it he was informed of the nearness of his death."  

عَنْ قَوْلِهِ تَعَالَى {إِذَا جَاءَ نَصْرُ اللَّهِ وَالْفَتْحُ} قَالُوا فَتْحُ الْمَدَائِنِ وَالْقُصُورِ قَالَ مَا تَقُولُ يَا ابْنَ عَبَّاسٍ قَالَ أَجَلٌ أَوْ مَثَلٌ ضُرِبَ لِمُحَمَّدٍ ﷺ نُعِيَتْ لَهُ نَفْسُهُ  

ʿUmar used to make me sit with the elderly men who had fought in the Battle of Badr. Some of them felt it (did not like that) and said to ʿUmar "Why do you bring in this boy to sit with us while we have sons like him?" ʿUmar replied, "Because of what you know of his position (i.e. his religious knowledge.)" One day ʿUmar called me and made me sit in the gathering of those people; and I think that he called me just to show them. (my religious knowledge). ʿUmar then asked them (in my presence). "What do you say about the interpretation of the Statement of Allah: 'When comes Help of Allah (to you O, Muhammad against your enemies) and the conquest (of Mecca).' (110.1) Some of them said, "We are ordered to praise Allah and ask for His forgiveness when Allah's Help and the conquest (of Mecca) comes to us." Some others kept quiet and did not say anything. On that, ʿUmar asked me, "Do you say the same, O Ibn ʿAbbas?" I replied, "No." He said, 'What do you say then?" I replied, "That is the sign of the death of Messenger of Allah ﷺ which Allah informed him of. Allah said:-- '(O Muhammad) When comes the Help of Allah (to you against your enemies) and the conquest (of Mecca) (which is the sign of your death). You should celebrate the praises of your Lord and ask for His Forgiveness, and He is the One Who accepts the repentance and forgives.' (110.3) On that ʿUmar said, "I do not know anything about it other than what you have said."  

كَانَ عُمَرُ يُدْخِلُنِي مَعَ أَشْيَاخِ بَدْرٍ فَكَأَنَّ بَعْضَهُمْ وَجَدَ فِي نَفْسِهِ فَقَالَ لِمَ تُدْخِلُ هَذَا مَعَنَا وَلَنَا أَبْنَاءٌ مِثْلُهُ فَقَالَ عُمَرُ إِنَّهُ مِنْ حَيْثُ عَلِمْتُمْ فَدَعَا ذَاتَ يَوْمٍ فَأَدْخَلَهُ مَعَهُمْ فَمَا رُئِيتُ أَنَّهُ دَعَانِي يَوْمَئِذٍ إِلاَّ لِيُرِيَهُمْ قَالَ مَا تَقُولُونَ فِي قَوْلِ اللَّهِ تَعَالَى {إِذَا جَاءَ نَصْرُ اللَّهِ وَالْفَتْحُ} فَقَالَ بَعْضُهُمْ أُمِرْنَا نَحْمَدُ اللَّهَ وَنَسْتَغْفِرُهُ إِذَا نُصِرْنَا وَفُتِحَ عَلَيْنَا وَسَكَتَ بَعْضُهُمْ فَلَمْ يَقُلْ شَيْئًا فَقَالَ لِي أَكَذَاكَ تَقُولُ يَا ابْنَ عَبَّاسٍ فَقُلْتُ لاَ قَالَ فَمَا تَقُولُ قُلْتُ هُوَ أَجَلُ رَسُولِ اللَّهِ ﷺ أَعْلَمَهُ لَهُ قَالَ {إِذَا جَاءَ نَصْرُ اللَّهِ وَالْفَتْحُ} وَذَلِكَ عَلاَمَةُ أَجَلِكَ {فَسَبِّحْ بِحَمْدِ رَبِّكَ وَاسْتَغْفِرْهُ إِنَّهُ كَانَ تَوَّابًا} فَقَالَ عُمَرُ مَا أَعْلَمُ مِنْهَا إِلاَّ مَا تَقُولُ