It was narrated that Malik bin Al-Huwairith said:
"I came to the Prophet (ﷺ) with a cousin of mine" - on an another occasion he said: "with a companion of mine" - "and he said: 'When the two of you travel, call the Adhan and the Iqamah, and let the older of you lead the prayer.'"
English reference: Vol. 1, Book 7, Hadith 635
Arabic reference: Book 7, Hadith 641