The Book of the Adhan (The Call to Prayer)
7/7. Chapter:
The Adhan Of Two Who Are Alone On A Journey
Sunan an-Nasai
أَخْبَرَنَا حَاجِبُ بْنُ سُلَيْمَانَ، عَنْ وَكِيعٍ، عَنْ سُفْيَانَ، عَنْ خَالِدٍ الْحَذَّاءِ، عَنْ أَبِي قِلاَبَةَ، عَنْ مَالِكِ بْنِ الْحُوَيْرِثِ، قَالَ أَتَيْتُ النَّبِيَّ صلى الله عليه وسلم أَنَا وَابْنُ عَمٍّ لِي وَقَالَ مَرَّةً أُخْرَى أَنَا وَصَاحِبٌ لِي فَقَالَ " إِذَا سَافَرْتُمَا فَأَذِّنَا وَأَقِيمَا وَلْيَؤُمَّكُمَا أَكْبَرُكُمَا " .
It was narrated that Malik bin Al-Huwairith said: "I came to the Prophet (S.A.W) 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.'"
Reference : Sunan an-Nasa'i 634In-book reference : Book 7, Hadith 9English translation : Vol. 1, Book 7, Hadith 635