Narrated 'Uthman bin 'Abdullah bin Mawhab:
"A man among the people of Egypt performed Hajj to the House, and saw a group sitting, so he said: 'Who are these?' They said: 'The Quraish.' He said: 'So who is this old man?' They said: 'Ibn 'Umar.' So he went to him and said: 'I will ask you about something, so inform me. I ask you by Allah! By the sanctity of this House! Do you know that 'Uthman fled on the Day of (the battle of) Uhud?' He said: 'Yes.' He said: 'Do you know that he was absent from the Pledge of Ar-Ridwan, that he did not witness it?' He said: 'Yes.' He said: 'Do you know that he was absent on the Day of (the battle of) Badr and did not participate in it?' He said: 'Yes.' So he said: 'Allah is Great' So Ibn 'Umar said to him: 'Come, so I can clarify to you what you have asked about. As for his fleeing on the Day of (the battle of) Uhud, then I bear witness that Allah has pardoned him and forgiven him. As for his being absent on the Day of (the battle of) Badr, then he was married to the daughter of the Messenger of Allah (ﷺ). So the Messenger of Allah (ﷺ) said to him: "You have the reward of a man who participated in (the battle of) Badr, and his share (spoils of war)." [And he ordered him to stay behind with her, as she was ill]. As for his being absent from the Pledge of Ar-Ridwan, then if there was anyone more revered in Makkah than 'Uthman, then the Messenger of Allah (ﷺ) would have sent him instead of 'Uthman. The Messenger of Allah (ﷺ) sent 'Uthman [to Makkah], and the Pledge of Ar-Ridwan was after 'Uthman had departed for Makkah." He said: "So the Messenger of Allah (ﷺ) said with his right hand: "This is the hand of 'Uthman," and he put it upon his own hand, and said: "This is for 'Uthman."' He said to him: "Go now, and take this (clarification) with you."
English reference: Vol. 1, Book 46, Hadith 3706
Arabic reference: Book 49, Hadith 4071