(18) باب الأَذَانِ لِلْمُسَافِرِ إِذَا كَانُوا جَمَاعَةً، وَالإِقَامَةِ، وَكَذَلِكَ بِعَرَفَةَ وَجَمْعٍ
Narrated Malik bin Huwairith:
Two men came to the Prophet (ﷺ) with the intention of a journey. The Prophet (ﷺ) said, "When (both of) you set out, pronounce Adhan and then Iqama and the oldest of you should lead the prayer."
Reference: Sahih al-Bukhari 630
In-book reference: Book 10, Hadith 27
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 11, Hadith 603