Musnad Abu Ya'la al-Mawsili 1:134

Narrated to us Muhriz ibn ‘Awn, narrated to us ‘Uthman ibn Matar, narrated to us ‘Abd al-Ghafur, from Abu Nasirah, from Abu Raja’, from Abu Bakr, from the Prophet (peace be upon him), who said: "Adhere to 'There is no god but Allah' (la ilaha illa Allah) and seeking forgiveness (istighfar), and increase in both of them. For Iblis said: 'I destroyed the people with sins, and they destroyed me with "There is no god but Allah" and seeking forgiveness.' So when I saw that, I destroyed them with desires (al-ahwa'), while they suppose that they are guided."