Musnad Abu Ya'la al-Mawsili 115:85

Ubayd Allah ibn Umar narrated to us, Mu'adh ibn Hisham narrated to us, my father narrated to me, from Qatadah, that Anas narrated that the Prophet of Allah, may Allah bless him and grant him peace, said: "It will be said to a man on the Day of Resurrection: 'Do you see, if you had the earth filled with gold, would you ransom yourself with it?' He will say: 'Yes.' It will be said to him: 'You were asked for something easier than that.'"