Is it Sunnah to Give Ādhān When Departing for a Journey?

The word “sunnah” and its derivatives are used in two senses:

1. That which is proven to have been the practice of RasūluLlāh ṣallaLlāhu ʿalayhi wa sallam;
2. That which is generally recommended. 

Adhān upon departure for a journey is not a proven prophetic sunnah. Rather, it is something desirable on account of the benefit of safety during the journey which it is believed to provide. This benefit rests upon experience. It is similar to the case of certain verses or sūrahs of the Qurʾān being prescribed for specific purposes. 

The lists of occasions on which adhān is recommended as contained in the books of the fuqahāʾ include both categories.

And Allah taʿālā knows best.