Did Prophet Muhammad s.a.a.s. ever sin?

Prophet Muhammad (s.a.a.s.) was human and made mistakes.  (e.g. the Qur'an reprimands him for turning away from an old man who asked him something while he was talking to a group of people)

However, his mistakes never amount to a "sin" (disobeying God or His commands) such as not praying, lying, stealing, etc.  Not even before his prophethood.   This makes sense because for him to be aware that God is watching his every action and communicating directly through him (the Quran being God's Words), how could he disobey Him?

One theory could be that all narrations about him cover up any such details. Part of the reason many thought he had gone "mad" rather than being simply a "liar" - because they could not understand how such a good person would preach  a message counter to their traditional way of life - Even his enemies had nothing bad to say of him (which rules out the above hypothesis).

Roman emperor Heraclius and his conversation with Abu Sufyan, leader of the Arab Pagans (both were enemies of the prophet during the conversation)

Heraclius said, "Bring him (Abu Sufyan) close to me and make his companions stand behind him." Abu Sufyan added, Heraclius told his translator to tell my companions that he wanted to put some questions to me regarding that man (The Prophet) and that if I told a lie they (my companions) should contradict me." Abu Sufyan added, "By Allah! Had I not been afraid of my companions labeling me a liar, I would not have spoken the truth about the Prophet. The first question he asked me about him was:
'What is his family status amongst you?'
I replied, 'He belongs to a good (noble) family amongst us.'
Heraclius further asked, 'Has anybody amongst you ever claimed the same (i.e. to be a Prophet) before him?'
I replied, 'No.'
He said, 'Was anybody amongst his ancestors a king?'
I replied, 'No.'
Heraclius asked, 'Do the nobles or the poor follow him?'
I replied, 'It is the poor who follow him.'
He said, 'Are his followers increasing decreasing (day by day)?'
I replied, 'They are increasing.'
He then asked, 'Does anybody amongst those who embrace his religion become displeased and renounce the religion afterwards?'
I replied, 'No.'
Heraclius said, 'Have you ever accused him of telling lies before his claim (to be a Prophet)?'
I replied, 'No.'
Heraclius said, 'Does he break his promises?'
I replied, 'No. We are at truce with him but we do not know what he will do in it.' I could not find opportunity to say anything against him except that.
Heraclius asked, 'Have you ever had a war with him?'
I replied, 'Yes.'
Then he said, 'What was the outcome of the battles?'
I replied, 'Sometimes he was victorious and sometimes we.'
Heraclius said, 'What does he order you to do?'
I said, 'He tells us to worship Allah and Allah alone and not to worship anything along with Him, and to renounce all that our ancestors had said. He orders us to pray, to speak the truth, to be chaste and to keep good relations with our kith and kin.'

Finally - there are hadith which may suggest he hadn't sinned (even though prophets in the past have been known to have sinned i.e. Jonah a.s. running away, Moses a.s. killing a man, David a.s. desiring another man's wife, Adam a.s. eating the forbidden fruit, etc - so its not impossible):
- all his past and future sins were forgiven

- on judgement day prophets starting from Adam a.s. will be asked by the people to ask God to

Judgment (because they will be tired of waiting).  Each prophet will refer the people to the next prophet due to a sin they had committed which they were ashamed of.  Finally the people will reach the final prophet Muhammad s.a.a.s. and he will ask (suggesting there was no sin to be ashamed of)

 

I will be the chief of all of Adams offspring on Resurection Day and I do no say this for boasting. I will hold the banner of praise and I do not say this for boasting. On that Day there is no prophet from Adam down but that he will be under my banner. I will be the first for whom the earth will split (exit the grave) and I do not say this for boasting. The people will panic three times. So they will go to Adam and say ‘You are our father so intercede for us with your Lord’ He will respond ‘Indeed I have commited a sin that resulted in my dropping to Earth. Go to Noah. They will go to Hoah and he will say ‘Indeed I made a curse against the people of Earth that resulted in their destruction. Go to Abraham. They will go to Abraham and he will say ‘I lied three times. Go to Moses. They will go to Moses and he will say ‘Indeed I killed a soul. Go to Jesus. They will go to Jesus and he will say ‘Indeed I was worshipped instead of God, Go to Muhammad. So they will come to me, and I will go with them. [Tirmidhi, authentic by albani]