Musnad Ahmad 31:254

Abu Salamah narrated to us, Layth informed us, from Yazid ibn al-Had, from ‘Amr, from Abu Sa’id al-Khudri, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, 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.' So Allah said to him: 'By My Might and My Majesty, I will not cease to forgive them as long as they seek My forgiveness.'"