Prophet Muhammad’s title before his prophet hood among his tribe was (the truthful the trust worthy).
It was very common that Muhammad peace be upon him never told a lie through his life and his reputation was beyond any question.
There are many situations that support that, one of them is: When the prophet peace be upon him gathered all of Qurish tribe and said to them : ( If I told you that there’s a huge army behind this mountain and they want to attack you, would you believe me?) They said : ( We never heard a lie out of you).
Then he said : ( I am a warner to you before the painful punishment comes). But the Arabs disbelievers didn’t believe out of arrogance, they never thought that prophet Muhammad is a liar.
God said:”” We know that you, [O Muhammad], are saddened by what they say. And indeed, they do not call you untruthful, but it is the verses of Allah that the wrongdoers reject.”” Chapter 6″(33)