Hawzah News Agency – The merciful prophet of Islam, peace be upon him and his household says:

المؤمنُ هَيِّنٌ لَيِّنٌ، حتّى‏ تَخالَهُ مِن اللِّينِ أحمقَ.

'The believer is nice and simple, such that he could be mistaken to be stupid because of his simplicity.'

Source: Kanz al-Ummal, no. 690