“Indeed, the number of months with Allah is 12 [lunar] months in the register of Allah [from] the day He created the heavens and the earth; of these, four are sacred.”
This ayah (Q9:36), on the twelve months and the four sacred ones, is the Qur'anic basis for the lunar calendar structure established at this event -- the very next verse (9:37) is cited in the event's own description regarding al-Nasi.
Establishes the sanctity of Dhu al-Qa'dah, the month in which the Prophet ﷺ deliberately timed this departure.