Majma al-Zawaid 11514 — Surah al-Zalzalah

Sayyiduna Anas (may Allah be pleased with him) narrates: Once Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) was eating with the Prophet (peace and blessings be upon him) when this verse was revealed to him: "And whoever does an atom's weight of good will see it (its reward), and whoever does an atom's weight of evil will see it (its recompense)." Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) withdrew his hand and said: O Messenger of Allah! Will I see the recompense even of the atom's weight of evil that I have done? The Prophet (peace and blessings be upon him) said: O Abu Bakr! Have you not considered that whatever (unpleasant) thing (or situation) you see in this world which you dislike is in proportion to the weights of evil (that is, it is the recompense for evil), while the weights of good are stored up for you until you are given their full reward on the Day of Resurrection?
Al-Tabarani recorded it in al-Mu'jam al-Awsat from his teacher Musa bin Sahl; it appears that he is al-Washsha', who is da'if (weak).