So do you accept the fact that you have no secular resources but only the own manuscripts themselves attest about themselves?
Okay tell me like Im a 3 year old what exactly your question is. You want secular sources for what? Muhammed or the Quran?
Quran, secular sources are manuscripts. Theological sources are completely different.
Muhammed, the earliest source is the Quran itself.
Historically there was a battle of Gabitha in the year 636, just four years after the prophet died. This was a battle between Arabs and Byzantines. You should do some research on a document written shortly after this war that mentions Muhammed. (Just FYI, the document was not written by a Muslim)
There was an Armenian Bishop (I think Sebeos) who mentions Muhammed written somewhere around 660 or shortly after.