Musnad Ahmad 482:51

Haywah ibn Shurayh narrated to us, he said: Baqiyyah narrated to us, Buhayr ibn Sa’d narrated to us, from Khalid ibn Ma’dan, from Jubayr ibn Nufayr, from ‘Uqbah ibn ‘Amir, that he said: A grey mule was gifted to the Messenger of Allah, may Allah bless him and grant him peace, so he rode it, and ‘Uqbah took to leading it for him. The Messenger of Allah, may Allah bless him and grant him peace, said to ‘Uqbah: "Recite." He said: "And what shall I recite, O Messenger of Allah?" The Prophet, may Allah bless him and grant him peace, said: "Recite: 'Say, I seek refuge in the Lord of the daybreak' (Qul a’udhu bi-rabbi al-falaq)." He repeated it to him until he recited it. He perceived that I was not very joyful with it, so he said: "Perhaps you took it lightly? For you have not stood to pray with anything like it."