There are legally punishable sin mentioned in Quran. For example adultery. But some hadith claims prophet withheld performing his duty as the leader of his community.

Sahih Bukhari Volume 008, Book 082, Hadith Number 812. Narrated By Anas bin Malik : While I was with the Prophet a man came and said, "O Allah's Apostle! I have committed a legally punishable sin; please inflict the legal punishment on me'.' The Prophet did not ask him what he had done. Then the time for the prayer became due and the man offered prayer along with the Prophet , and when the Prophet had finished his prayer, the man again got up and said, "O Allah's Apostle! I have committed a legally punishable sin; please inflict the punishment on me according to Allah's Laws." The Prophet said, "Haven't you prayed with us?' He said, "Yes." The Prophet said, "Allah has forgiven your sin." or said, "...your legally punishable sin."

This hadith is problematic. How can prophet knew someones sin is forgiven by Allah or vice versa ?

I am no different from the other messengers, nor do I know what will happen to me or to you. I only follow what is inspired to me. I am no more than a clear warner" [Quran 46:9]