Musnad Ahmad 132:16

Hassan narrated to us, Ibn Lahi'ah narrated to us, Zaban bin Fa'id narrated to us, from Sahl, from his father, from the Messenger of Allah, peace and blessings of Allah be upon him, that he said: "Shall I not inform you why Allah, Blessed and Exalted is He, named Ibrahim His 'Khalil' (Intimate Friend) who fulfilled? Because he used to say, whenever he reached the morning and the evening: 'So exalted is Allah when you reach the evening and when you reach the morning' [Ar-Rum: 17], until he completed the verse."