Musnad Ahmad 32:392

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, he said: I heard Abu Hamzah, our neighbor, narrating from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said to Mu'adh ibn Jabal: "Know that whoever dies testifying that there is no god but Allah, will enter Paradise."