Musnad Abu Ya'la al-Mawsili 115:136

Abu Khaythama narrated to us, Mu'adh ibn Hisham narrated to us, my father narrated to me, from Qatada, from Anas, that the Prophet of Allah (may Allah bless him and grant him peace) said: "He shall be brought out of the Fire who said 'There is no god but Allah,' and there was in his heart of goodness what weighs a barleycorn. Then he shall be brought out of the Fire who said 'There is no god but Allah,' and there was in his heart of goodness what weighs a wheat grain. Then he shall be brought out of the Fire who said 'There is no god but Allah,' and there was in his heart of goodness what weighs an atom."