Was the Battle of Tabuk an aggression, not a defense, and did the Romans not pose a threat to the Muslims?

The assertion that the Byzantines (Romans) did not pose a threat to Muslims before the Battle of Tabuk is false for several reasons, including:

1. The Byzantines (Romans) massed and mobilized their forces against the Muslims. Some have mentioned that Christianized Arabs wrote to Heraclius, informing him that the Prophet (peace be upon him) had passed away, so he prepared an army of forty thousand men. 2. The killing of the Prophet's (peace be upon him) envoy, Al-Harith ibn Umayr Al-Azdi, by Shurahbil ibn Amr Al-Ghassani, and the subsequent Battle of Mu'tah, in which the Muslims were unable to avenge themselves. Caesar (Heraclius) saw this as a threat to the frontiers of Sham (Greater Syria) and began preparing an army to confront the Muslims.