Musnad Ahmad 25:491

Ubaydah ibn Humayd narrated to us, Yazid ibn Abi Ziyad narrated to us, from a man, from Ibn Abbas, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) was on a journey, and he halted for the night, so he slept and did not wake up until the sun [had risen]." He said: "The Messenger of Allah (peace and blessings of Allah be upon him) ordered Bilal, so he gave the adhan, and he prayed two rak'ahs." Ibn Abbas said: "The world and all that is in it does not please me more than it [meaning the concession]."