Objection for fleeing from the Battle of Uhud
Those who criticise Sayyiduna `Uthman ibn `Affan radiya Llahu `anhu have mentioned that in the Battle of Uhud, Sayyiduna `Uthman ibn `Affan radiya Llahu `anhu was among those Sahabah who fled from the battlefield; and it is forbidden in Islam to flee the battlefield.
The senior scholars of history have mentioned that in the Battle of Uhud, Rasulullah salla Llahu `alayhi wa sallam deputed a group of archers on a hill with the instruction not to leave their position under any circumstances. However, the battle quickly turned in favour of the Muslims, and having perceived this to be a victory (and end of the battle), a group of these archers left their position and participated in gathering the spoils of war. While in this condition, the disbelievers led a severe counterattack from this unguarded position. It was in this perilous time that some of the Muslims were shaken and left the battlefield. Among them was Sayyiduna `Uthman ibn `Affan radiya Llahu `anhu.
Allah has mentioned this incident in the Qur’an briefly, expressing His Forgiveness for having slipped at this juncture:
إِنَّ الَّذِيْنَ تَوَلَّوْا مِنْكُمْ يَوْمَ الْتَقَى الْجَمْعَانِۙ إِنَّمَا اسْتَزَلَّهُمُ الشَّيْطَانُ بِبَعْضِ مَا كَسَبُواۚ وَلَقَدْ عَفَا اللّٰهُ عَنْهُمْؕ إِنَّ اللّٰهَ غَفُورٌ حَلِيمٌ
Indeed, those of you who turned back on the day the two armies met, it was Shaytan who caused them to slip because of some (blame) they had earned. But Allah has already forgiven them. Indeed, Allah is Forgiving and Forbearing.
In short, from whoever this slip up occurred, including Sayyiduna `Uthman ibn `Affan radiya Llahu `anhu, Allah forgave them. Now there is no sin on them as Allah has forgiven them completely. No person now has the right to criticise them, nor is there any permissibility to rebuke them.
 Surah Al-`Imran: 155