Musnad Ahmad 209
It was narrated that 'Umar bin al­-Khattab (رضي الله عنه ­) said:
We were with the Messenger of Allah (ﷺ)  on a journey, and I asked him about something three times but he did not answer me. I said to myself, May 
your mother be bereft of you. O son of al-Khattab, you spoke to the Messenger of Allah (ﷺ) three times and he did not answer you. So I got on my mount and went on ahead, fearing that something had been revealed concerning me. Then I heard someone calling out: O 'Umar! Where is ‘Umar? I went back, thinking that something had been revealed concerning me, and the Prophet (ﷺ) said: `Yesterday a soorah was revealed to me that is dearer to me than this world and everything in it: ‘Verily, We have given you (O Muhammad ﷺ) a manifest victory. That Atlah may forgive you your sins of the past and the future' (al­-Fath 48:1–2].
حَدَّثَنَا أَبُو نُوحٍ، حَدَّثَنَا مَالِكُ بْنُ أَنَسٍ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ أَبِيهِ، عَنْ عُمَرَ بْنِ الْخَطَّابِ، رَضِيَ اللَّهُ عَنْهُ قَالَ كُنَّا مَعَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي سَفَرٍ قَالَ فَسَأَلْتُهُ عَنْ شَيْءٍ ثَلَاثَ مَرَّاتٍ فَلَمْ يَرُدَّ عَلَيَّ قَالَ فَقُلْتُ لِنَفْسِي ثَكِلَتْكَ أُمُّكَ يَا ابْنَ الْخَطَّابِ نَزَرْتَ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ ثَلَاثَ مَرَّاتٍ فَلَمْ يَرُدَّ عَلَيْكَ قَالَ فَرَكِبْتُ رَاحِلَتِي فَتَقَدَّمْتُ مَخَافَةَ أَنْ يَكُونَ نَزَلَ فِيَّ شَيْءٌ قَالَ فَإِذَا أَنَا بِمُنَادٍ يُنَادِي يَا عُمَرُ أَيْنَ عُمَرُ قَالَ فَرَجَعْتُ وَأَنَا أَظُنُّ أَنَّهُ نَزَلَ فِيَّ شَيْءٌ قَالَ فَقَالَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ نَزَلَتْ عَلَيَّ الْبَارِحَةَ سُورَةٌ هِيَ أَحَبُّ إِلَيَّ مِنْ الدُّنْيَا وَمَا فِيهَا إِنَّا فَتَحْنَا لَكَ فَتْحًا مُبِينًا لِيَغْفِرَ لَكَ اللَّهُ مَا تَقَدَّمَ مِنْ ذَنْبِكَ وَمَا تَأَخَّرَ‏.‏