Musnad Abu Ya'la al-Mawsili 116:14

Ahmad narrated to us, Abu Dawud narrated to us, Shu'bah narrated to us, from Qatadah, from Anas, that the Prophet (may Allah bless him and grant him peace) said to Mu'adh: "Know that whoever dies while testifying that there is no god but Allah and that Muhammad is the Messenger of Allah, sincerely from his heart, will enter Paradise."