Musnad Abu Ya'la al-Mawsili 152:212

Abu Khaythama narrated to us, Abd al-Rahman narrated to us, from Sufyan, from Mansur and al-A'mash, from Abu Wa'il, from Abdullah, from the Prophet (peace and blessings of Allah be upon him), who said: "Paradise is closer to one of you than the strap of his sandal, and the Fire is likewise."