Narrated 'Uthman bin Mauhab:

A man came to perform the Hajj to (Allah's) House. Seeing some people sitting, he said, "Who are these sitting people?" Somebody said, "They are the people of Quraish." He said, "Who is the old man?" They said, "Ibn 'Umar." He went to him and said, "I want to ask you about something;
will you tell me about it? I ask you with the respect due to the sanctity of this (Sacred) House, do you know that 'Uthman bin 'Affan fled on the day of Uhud?" Ibn 'Umar said, "Yes." He said, "Do you know that he (i.e. 'Uthman) was absent from the Badr (battle) and did not join it?" Ibn 'Umar said, "Yes." He said, "Do you know that he failed to be present at the Ridwan Pledge of allegiance (i.e. Pledge of allegiance at Hudaibiya) and did not witness it?" Ibn 'Umar replied, "Yes," He then said, "Allahu-Akbar!" Ibn 'Umar said, "Come along;
I will inform you and explain to you what you have asked. As for the flight (of 'Uthman) on the day of Uhud, I testify that Allah forgave him. As regards his absence from the Badr (battle), he was married to the daughter of Allah's Apostle and she was ill, so the Prophet ﷺ said to him, 'You will have such reward as a man who has fought the Badr battle will get, and will also have the same share of the booty.' As for his absence from the Ridwan Pledge of allegiance if there had been anybody more respected by the Meccans than 'Uthman bin 'Affan, the Prophet would surely have sent that man instead of 'Uthman. So the Prophet sent him (i.e. 'Uthman to Mecca) and the Ridwan Pledge of allegiance took place after 'Uthman had gone to Mecca. The Prophet raised his right hand saying. 'This is the hand of 'Uthman,' and clapped it over his other hand and said, "This is for 'Uthman.'" Ibn 'Umar then said (to the man), "Go now, after taking this information."

حَدَّثَنَا عَبْدَانُ، أَخْبَرَنَا أَبُو حَمْزَةَ، عَنْ عُثْمَانَ بْنِ مَوْهَبٍ، قَالَ جَاءَ رَجُلٌ حَجَّ الْبَيْتَ فَرَأَى قَوْمًا جُلُوسًا فَقَالَ مَنْ هَؤُلاَءِ الْقُعُودُ قَالُوا هَؤُلاَءِ قُرَيْشٌ. قَالَ مَنِ الشَّيْخُ قَالُوا ابْنُ عُمَرَ. فَأَتَاهُ فَقَالَ إِنِّي سَائِلُكَ عَنْ شَىْءٍ أَتُحَدِّثُنِي، قَالَ أَنْشُدُكَ بِحُرْمَةِ هَذَا الْبَيْتِ أَتَعْلَمُ أَنَّ عُثْمَانَ بْنَ عَفَّانَ فَرَّ يَوْمَ أُحُدٍ قَالَ نَعَمْ. قَالَ فَتَعْلَمُهُ تَغَيَّبَ عَنْ بَدْرٍ فَلَمْ يَشْهَدْهَا قَالَ نَعَمْ. قَالَ فَتَعْلَمُ أَنَّهُ تَخَلَّفَ عَنْ بَيْعَةِ الرُّضْوَانِ فَلَمْ يَشْهَدْهَا قَالَ نَعَمْ. قَالَ فَكَبَّرَ. قَالَ ابْنُ عُمَرَ تَعَالَ لأُخْبِرَكَ وَلأُبَيِّنَ لَكَ عَمَّا سَأَلْتَنِي عَنْهُ، أَمَّا فِرَارُهُ يَوْمَ أُحُدٍ فَأَشْهَدُ أَنَّ اللَّهَ عَفَا عَنْهُ، وَأَمَّا تَغَيُّبُهُ عَنْ بَدْرٍ فَإِنَّهُ كَانَ تَحْتَهُ بِنْتُ رَسُولِ اللَّهِ ﷺ وَكَانَتْ مَرِيضَةً، فَقَالَ لَهُ النَّبِيُّ ﷺ " إِنَّ لَكَ أَجْرَ رَجُلٍ مِمَّنْ شَهِدَ بَدْرًا وَسَهْمَهُ ". وَأَمَّا تَغَيُّبُهُ عَنْ بَيْعَةِ الرُّضْوَانِ فَإِنَّهُ لَوْ كَانَ أَحَدٌ أَعَزَّ بِبَطْنِ مَكَّةَ مِنْ عُثْمَانَ بْنِ عَفَّانَ لَبَعَثَهُ مَكَانَهُ، فَبَعَثَ عُثْمَانَ، وَكَانَ بَيْعَةُ الرُّضْوَانِ بَعْدَ مَا ذَهَبَ عُثْمَانُ إِلَى مَكَّةَ فَقَالَ النَّبِيُّ ﷺ بِيَدِهِ الْيُمْنَى " هَذِهِ يَدُ عُثْمَانَ ". فَضَرَبَ بِهَا عَلَى يَدِهِ فَقَالَ " هَذِهِ لِعُثْمَانَ ". اذْهَبْ بِهَذَا الآنَ مَعَكَ.