I came to the Prophet ﷺ together with a cousin of mine, and on another occasion he said, with a companion of mine. The Prophet ﷺ said, "When the two of you travel, give the call to prayer and the iqamah, and let the elder of you lead the prayer."
أخبرنا حاجب بن سليمان عن وكيع عن سفيان عن خالد الحذاء عن أبي قلابة
أتيت النبي ﷺ أنا وابن عم لي وقال مرة أخرى أنا وصاحب لي فقال إذا سافرتما فأذنا وأقيما وليؤمكما أكبركما
Bukhari included it in the Book of Adhan, chapter on the adhan for travelers when they are in a group and the iqamah etc., hadith no. 630, from the hadith of Sufyan Thawri. Muslim included it in the Book of Mosques, chapter on who is most entitled to lead the prayer, hadith no. 674/293, from the hadith of Khalid Haddan, with the same wording. It is also in al-Kubra, hadith no. 1598. Tirmidhi included it, hadith no. 205, from the hadith of Waki, with the same wording.