It was narrated from Abdur-Rahman bin ‘Awf that

some people of the Arabs came to the Messenger of Allah (ﷺ) in Madinah and became Muslim, and they fell sick with the sickness (fever) of Madinah. They fell sick and left Madinah, and were met by a group of his companions -meaning Companions of the Prophet who said to them: why are you leaving? They said we have got the fever of Madinah so we decided to leave Madinah. They said: Don"t you have a good example in the Messenger of Allah? Some of them (the companions) said : They have become hypocrites and some of them said they have not become hypocrites and they are still Muslims. Then Allah, may He be glorified and exalted, revealed the verse: "Then what is the matter with you that you are divided into two - parties about the hypocrites? Allah has cast them back (to disbelief) because of what they have earned" [an-Nisa" 4:88).