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 <i>adhan</i> and repeat the <i>iqama</i>, then the older of you should act as <i>imam</i>.” This is how Bukhari transmitted it.

وَعَن مَالك بن الْحُوَيْرِث قَالَ: أَتَيْتُ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَنَا وَابْنُ عَمٍّ لِي فَقَالَ: «إِذَا سَافَرْتُمَا فأذنا وأقيما وليؤمكما أكبركما» . رَوَاهُ البُخَارِيّ