The earliest biography we have of Muhammad is from ibn hisham who compiled and edited (removing large parts of) ibn ishaq's work, life of the prophet. This document is over 200 years after Mohammad died and contains many things which contradicts the Quran, hadiths, tafsirs, and modern Islam.
The earliest coins
Mecca doesn't appear on any map until centuries later.
The earliest inscriptions of Muhammad appears to be of Jesus