Malik b. al-Huwairith said that he and a cousin of his came to the Prophet, who said, “When you two are on a journey, you should call the adhan and repeat the iqama, then the older of you should act as imam.” This is how Bukhari transmitted it.
Hadith Referenceمشكوة المصابيح / كتاب الصلاة / 682
Hadith Gradingالألبانی:صَحِيح | زبیر علی زئی:صحيح
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «رواه البخاري (628) [و مسلم 674/293]»