Abdullah bin Abbas reported,

Umar used to bring me into the gatherings of the elders of Badr. Some of them objected, saying, "Why do you bring this young man in with us when we have sons his age?"Umar replied, "He is one whose standing you already know."One day he summoned them and called me along with them. I did not see him call me on that occasion except to display my knowledge to them. He asked, "What do you say about 'When the help of Allah comes and the victory, and you see the people entering the religion of Allah in crowds'[Nasr 110:1–2]?" until he finished the surah.Some of them said, "We are commanded to praise Allah and seek His forgiveness when He grants us help and victory."Others said, "We do not know," or said nothing at all.Then he said to me, "Ibn Abbas, do you say the same?"I said, "No."He asked, "Then what do you say?"I said, "It refers to the appointed end of the Messenger of Allah ﷺ. Allah was informing him of it. 'When the help of Allah comes and the victory' refers to the conquest of Makkah, and that is the sign of your appointed end. 'So glorify the praise of your Lord and seek His forgiveness. Indeed, He is ever Accepting of repentance'[Nasr 110:3]."Umar said, "I know nothing of it except what you know."

Bukhari 4294

Sahih

حدثنا أبو النعمان حدثنا أبو عوانة عن أبي بشر عن سعيد بن جبير

عن ابن عباس رضي الله عنهما قال

كان عمر يدخلني مع أشياخ بدر فقال بعضهم لم تدخل هذا الفتى معنا ولنا أبناء مثله فقال إنه ممن قد علمتم قال فدعاهم ذات يوم ودعاني معهم قال وما رئيته دعاني يومئذ إلا ليريهم مني فقال ما تقولون في {إذا جاء نصر الله والفتح ورأيت الناس يدخلون في دين الله أفواجا} حتى ختم السورة فقال بعضهم أمرنا أن نحمد الله ونستغفره إذا نصرنا وفتح علينا وقال بعضهم لا ندري أو لم يقل بعضهم شيئا فقال لي يا ابن عباس أكذاك تقول قلت لا قال فما تقول قلت هو أجل رسول الله ﷺ أعلمه الله له {إذا جاء نصر الله والفتح} فتح مكة فذاك علامة أجلك {فسبح بحمد ربك واستغفره إنه كان توابا} قال عمر ما أعلم منها إلا ما تعلم

البخاري 4294صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Bukhari
Book
Expeditions
Chapter
Prophet's ﷺ camp on the day of the conquest
Numbering
Darussalam 4294
Bukhari 4294