Mishkat al-Masabih 25

Anas ibn Malik reported that the Prophet, with Muadh riding behind him on the saddle, said, “Muadh ibn Jabal!” He replied, “At your service, Messenger of God, and ready to obey!” He said, “Muadh!” He replied, “At your service, Messenger of God, and ready to obey!” He called him three times. He then said, “There is no one who testifies sincerely from his heart that there is no god but God and that Muhammad is the Messenger of God but God will forbid the Fire to him.” Muadh said, “Messenger of God, shall I tell the people so they may rejoice?” He said, “Then they would rely on it.” Muadh told them of it at the time of his death, out of fear of sin.