Sahih al-Bukhari Book 10, Hadith 28
We came to the Prophet (ﷺ) and stayed with him for twenty days and nights. We were all young and of
about the same age. The Prophet (ﷺ) was very kind and merciful. When he realized our longing for our
families, he asked about our homes and the people there and we told him. Then he asked us to go back
to our families and stay with them and teach them (the religion) and to order them to do good things.
He also mentioned some other things which I have (remembered or ) forgotten. The Prophet (ﷺ) then
added, "Pray as you have seen me praying and when it is the time for the prayer one of you should
pronounce the Adhan and the oldest of you should lead the prayer.
Two men came to the Prophet (ﷺ) with the intention of a journey. The Prophet (ﷺ) said, "When (both of) you set out, pronounce Adhan and then Iqama and the oldest of you should lead the prayer."
Once in a cold night, Ibn `Umar pronounced the Adhan for the prayer at Dajnan (the name of a mountain) and then said, "Pray at your homes", and informed us that Allah's Messenger (ﷺ) used to tell the Mu'adh-dhin to pronounce Adhan and say, "Pray at your homes" at the end of the Adhan on a rainy or a very cold night during the journey."