Abu Salama bin Abdul-Rahman bin Awf reported,
Uthman 
looked down from the palace while he was under siege and said, "I ask you by Allah, who among you witnessed the Messenger of Allah ﷺ on the day of Hira when the mountain shook, and he kicked it with his foot and said, 'Be still, Hira, for there is none upon you but a Prophet, a truthful one, or a martyr,' and I was with him?"Some men testified for him.He said, "I ask you by Allah, who among you witnessed the Messenger of Allah ﷺ on the day of the Pledge of Ridwan, when he sent me to the polytheists, to the people of Mecca, and said, 'This is my hand and this is the hand of Uthman ,' and pledged allegiance on my behalf?"Some men testified for him.He said, "I ask you by Allah, who among you witnessed the Messenger of Allah ﷺ when he said, 'Who will expand the mosque for us by adding this house, in exchange for a house in Paradise?' So I bought it with my own wealth and used it to expand the mosque."Some men testified for him.He said, "I ask you by Allah, who among you witnessed the Messenger of Allah ﷺ on the day of the Army of Hardship, when he said, 'Who will spend today a contribution that will be accepted?' So I equipped half of the army from my own wealth."Some men testified for him.He said, "I ask you by Allah, who among you witnessed Rumah, when its water was being sold to the wayfarer, and I bought it with my own wealth and made it free for the wayfarer?"Some men testified for him.
Ahmad 420
Sahihحدثنا أبو قطن حدثنا يونس يعني ابن أبي إسحاق عن أبيه
عن أبي سلمة بن عبد الرحمن قال
أشرف عثمان رضي الله عنه من القصر وهو محصور فقال أنشد بالله من شهد رسول الله ﷺ يوم حراء إذ اهتز الجبل فركله بقدمه ثم قال اسكن حراء ليس عليك إلا نبي أو صديق أو شهيد وأنا معه فانتشد له رجال قال أنشد بالله من شهد رسول الله ﷺ يوم بيعة الرضوان إذ بعثني إلى المشركين إلى أهل مكة قال هذه يدي وهذه يد عثمان رضي الله عنه فبايع لي فانتشد له رجال قال أنشد بالله من شهد رسول الله ﷺ قال من يوسع لنا بهذا البيت في المسجد ببيت في الجنة فابتعته من مالي فوسعت به المسجد فانتشد له رجال قال وأنشد بالله من شهد رسول الله ﷺ يوم جيش العسرة قال من ينفق اليوم نفقة متقبلة فجهزت نصف الجيش من مالي قال فانتشد له رجال وأنشد بالله من شهد رومة يباع ماؤها ابن السبيل فابتعتها من مالي فأبحتها لابن السبيل قال فانتشد له رجال
Its isnad is sahih, except that they have discussed whether Abu Salama bin Abdul-Rahman actually heard from Talha and from Ubada bin Samit. Hafiz said in Tahdhib, "And even if that were the case, then he also did not hear from Uthman nor from Abu Darda, for each of them died before Talha." I have established the soundness of his hearing from Uthman in no. 1403.Abu Qatan, with two fathas, is Amr bin al-Haytham bin Qatan, and he is trustworthy. Yunus is the son of Abu Ishaq Sabi. This hadith was narrated by Nasai, 2/124-125, through the route of Isa bin Yunus, from his father, with this isnad. He then narrated it through the route of Zayd bin Abu Unaysa, from Abu Ishaq, from Abu Abdul-Rahman Sulami, from Uthman. Tirmidhi narrated it likewise, 4/319-320, and said, "This is a hasan sahih hadith, rare in this form, coming from the hadith of Abu Abdul-Rahman Sulami from Uthman." It seems, then, that Abu Ishaq Sabi heard it both from Abu Abdul-Rahman Sulami and from Abu Salama bin Abdul-Rahman.The word is written "fa-anshada" in this form in all the manuscript copies and in Nihaya as well, which states, regarding the hadith of Uthman, "So men answered him (fa-anshada lahu rijalun)," meaning they responded to him. It is said, "nashadtuhu fa-anshadani" and "anshada li," meaning "I asked him and he answered me." This alif is called "the alif of removal." It is said, "qasata al-rajulu" when a man acts unjustly, and "aqsata" when he acts justly, as though the alif removed his injustice. Likewise here, it removes the sense of asking, turning it into an answer.See no. 511.