Musnad Ahmad 482:127

Abu Abd al-Rahman narrated to us, Haywah and Ibn Lahi'ah narrated to us, they said: We heard Yazid ibn Abi Habib saying: Abu Imran narrated to me that he heard Uqbah ibn Amir saying: I clung to the foot of the Messenger of Allah, may Allah bless him and grant him peace, and said: "O Messenger of Allah, teach me Surah Hud and Surah Yusuf." The Messenger of Allah, may Allah bless him and grant him peace, said to me: "O Uqbah ibn Amir, you will not recite a surah more beloved to Allah, nor more profound in His sight, than 'Say: I seek refuge in the Lord of the daybreak' (Al-Falaq)." Yazid said: "Abu Imran would not abandon it, and he would always recite it in the Maghrib prayer."