Sahih Bukhari
To make the Heart Tender (Ar-Riqaq)
Volume: 008 / Book Number: 076 / Hadith Number: 562
Narrated Anas bin Malik:
The Prophet said, "Allah will say to the person who will have the minimum punishment in the Fire on the Day of Resurrection, 'If you had things equal to whatever is on the earth, would you ransom yourself (from the punishment) with it?' He will reply, Yes. Allah will say, 'I asked you a much easier thing than this while you were in the backbone of Adam, that is, not to worship others besides Me, but you refused and insisted to worship others besides Me."'