It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that he (peace and blessings be upon him) went to visit a Bedouin, and whenever he (peace and blessings be upon him) went to visit someone he would say: 'La ba's, tahurun in sha' Allah ta'ala' (No harm; it is a purification, if Allah Almighty wills). The man said: You say purification? Rather, this is a fever boiling over an old man, which will make him visit the graves. So the Prophet (peace and blessings be upon him) said: "Then so it is."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6595