Parashas Bo · Passuk 13:4
Chabad.org — English translation + Rashi
Torah Temimah points to Mechilta, Pesach section 16 (verified).
English: The month of the Exodus was a fit month for travel, neither harsh heat nor rains.
In context: See the cited source for the full section.
Derash on the verse.
The Exodus took place in a month suitable for travel.