Musnad Ahmad 30:3521

Aswad narrated to us, Abu Bakr informed us, from al-A’mash, from Abu Salih, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Every person of the Fire sees his seat in Paradise, and he says: 'Had Allah guided me.' So it becomes a source of regret for him." He said: "And every person of Paradise sees his seat in the Fire, and he says: 'Had it not been that Allah guided me.' He said: So it becomes a source of gratitude for him."