Sunan An-Nasa'i

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