Abu Zur'ah al-Bustani narrates: I went with my father and some other people to visit Sayyiduna Abu al-Darda' (may Allah be pleased with him). He was at that time in a house whose walls had become old (or weak), and he was facing the wall. We found his wife by his head. The people asked the woman: "How did Sayyiduna Abu al-Darda' (may Allah be pleased with him) spend the night?" The woman replied: "He spent the night with reward." Sayyiduna Abu al-Darda' (may Allah be pleased with him) turned his face towards us and said: "The truth is not what this woman has said." The people were taken aback at this. Sayyiduna Abu al-Darda' (may Allah be pleased with him) said: "Will you not ask me why I said this?" The people said: "Why did you say this?" He said: I heard the Prophet (peace and blessings be upon him) say: "When a believer falls ill, he is not rewarded because of the illness; rather, (sins) are removed from him."
Al-Tabarani recorded it in al-Mu'jam al-Kabir. Its chain contains a narrator, Hafs bin Umar bin Abi al-Qasim; I have not found anyone who mentions him. The remaining narrators of this report are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجنائز / 3789