It was narrated from Abu Hurayrah (may Allaah be pleased with him) that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Do not revile my companions, for by the One in Whose hand is my soul, if one of you were to spend the equivalent of Uhud in gold, it would not amount to a mudd of one of them, or half of that.” Narrated by al-Bukhaari (3673) and Muslim (2540).
You cannot be critical of any Sahabi, let alone Zun-Noorain, one of the Khulafa ar-Rashideen, one of the 'Ashara Mubashshira, the son-in-law of Rasulullah :saws:, the friend and companion of Rasulullah :saws: in this life as well as in Jannah.
'Uthman bin 'Affan :ra: is the only Sahabi whom Allah's Messenger :saws: gave his two daughters in marriage, and when the second one died, Rasulullah :saws: said, if I had another daughter, I would have given her in your hand.
He is one of those whom Rasulullah :saws: had given the glad tidings of Paradise.
At the time of the battle of Tabouk, 'Uthman :ra: supplied the army with nine hundred and forty camels, and sixty horses to bring the number to one thousand. 'Uthman :ra: brought ten thousand dinars to equip the army and placed the money before the Messenger of Allah :saws: and Rasulullah :saws: began turning it over with his hand saying, “No deed can harm ‘Uthman after today, No deed can harm ‘Uthman after today”. Sunan at-Tirmidhi
It was narrated from ‘Abd-Allah ibn ‘Aamir, from al-Nu’man ibn Basheer, that ‘Aa’ishah :raha: said: The Messenger of Allah :saws: sent for ‘Uthman ibn ‘Affan :ra: and the Messenger of Allah :saws: went to him and spoke with him. When we saw the Messenger of Allah :saws: we turned to one another, and the last thing he said to him was when he struck him on the shoulder and said:
"O ‘Uthman, Allah will give you a garment to wear (i.e., the caliphate), so if the hypocrites want you to shed it, do not shed it until you meet me."
Fada’il al-Sahabah, 1/206. Its isnad is saheeh Al-Musnad (6/52)
It was narrated that Murrah al-Bahzi said: I was with the Messenger of Allah :saws: and Bahz – one of the narrators of the hadeeth – said: The Messenger of Allah :saws: said:
“There will be turmoil like the horns of cows, but this man and those who are with him will be following the truth”
I went and grabbed him by his cloak, and saw that it was ‘Uthman ibn ‘Affan :ra:.
Musnad Ahmad, Musnad al-Shamiyeen, Bab Hadeeth Ka’b ibn Murrah al-Sulami aw Murrah ibn Ka’b, hadeeth no 17602 (4/236)