once
لاَ بأْسَ طَهُورٌ إِنْ شَاءَ اللَّهُ
Edition transliteration
La ba'sa tahoorun in shaal-lah.
Meaning
Never mind, may it (the sickness) be a purification, if Allah wills.
Source and references
Hisn al-Muslim, entry 147.The reference is copied from the edition; separate editorial verification is not complete yet.
Source edition: Fortress of the Muslim. Open source ↗