Musnad Abu Ya'la al-Mawsili 42:300

And from Yazid, from ‘Amr, from Abu Sa’id, who said: I heard the Messenger of Allah, may Allah bless him and grant him peace, say: "Indeed, Iblis said to his Lord: 'By Your Might and Your Majesty, I will not cease to lead the children of Adam astray as long as their souls are within them.' His Lord said to him: 'By My Might and My Majesty, I will not cease to forgive them as long as they seek My forgiveness.'"