It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that Allah Almighty says: "I test My believing servant, and when he does not complain of that to those who visit him, I untie My knot from him and replace his blood with better blood and his flesh with better flesh. Then I say to him: 'Now begin your deeds afresh.'"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6549