It is narrated from Sayyiduna Anas (may Allah be pleased with him) that Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) was eating with the Messenger of Allah (peace and blessings be upon him) when this verse was revealed to him (peace and blessings be upon him): "So whoever does an atom's weight of good will see it, and whoever does an atom's weight of evil will see it." Sayyiduna Abu Bakr (may Allah be pleased with him) held back his hand and said: "O Messenger of Allah (peace and blessings be upon him)! Will I see even the atom's weight of evil that I have done?" He (peace and blessings be upon him) said: "O Abu Bakr! The disliked things that befall you in this world are nothing but the recompense for atoms' weight of evil, and the atoms' weight of good is kept safe for you until you are given its full reward on the Day of Resurrection."
Imam al-Tabarani (may Allah have mercy on him) said: "No one narrated this hadith from Ayyub (may Allah have mercy on him) except Simak bin Atiyyah (may Allah have mercy on him), and no one narrated it from Simak (may Allah have mercy on him) except al-Haytham (may Allah have mercy on him); Ziyad bin Yahya (may Allah have mercy on him) is alone in narrating it."
Hadith Referenceالمعجم الأوسط / باب الميم / 8407
Hadith Gradingمحدثین:إسناده ضعيف لضعف موسى بن سهل الوشاء
Hadith Takhrij«قال الهيثمي: رواه الطبراني في الأوسط عن شيخه موسى بن سهل والظاهر أنه الوشاء وهو ضعيف «مجمع الزوائد ومنبع الفوائد، ج 7، ص 142»» «أخرجه الضياء المقدسي فى «الأحاديث المختارة» برقم: 2243، 2244»