This is a question christans ask themselves when they are faced with a dilemma. What exactly? Then they say or do as they feel; many times this would not be what others would do; seldomn do they agree. So really this question is a stab in the dark; hoping in vain.
As for the Muslim he does not have to ponder what Muhammad (peace and blessings of Allah be upon him) did. All he has to do is open a book about a certain subject and read. He can read a book about subjects of the heart, prayer or acts or worship etc. We have such an amazing wealth of information that reading it would take years. Even if goes straight to hadith like the collection of authentic narrations of Bukhari. The collection is nine volumes, nine large volumes that is not to consider other collections which compliment this one. We have libaries of information.
So we don't ask what would he do; we ask what did he do.