It is narrated from Sayyiduna Imran bin Husayn (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) was on a journey, and the people slept through the Fajr prayer and woke up in the heat of the sun. They moved on a little until the sun had risen high, then he (peace and blessings be upon him) ordered a mu'adhdhin, who called the adhan, and he (peace and blessings be upon him) prayed two rak'ahs before Fajr; then the iqamah was called and he led the Fajr prayer.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15423