«كان إذا دخل على مريض يعوده قال: لا بأس طهور إن شاء الله»
It was the practice of the Prophet (peace and blessings be upon him):
"When he (peace and blessings be upon him) went to visit a sick person, he would say: No harm; if Allah wills, this illness is a purification (washing away sins)."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4718