Musnad Ahmad 32:849

Mu'ammal narrated to us, Hammad narrated to us, Thabit narrated to us, from Anas, that a Jewish boy used to prepare the water for ablution for the Prophet, may Allah bless him and grant him peace, and hand him his sandals. He became ill, so the Prophet, may Allah bless him and grant him peace, came to him and entered upon him, while his father was sitting at his head. The Prophet, may Allah bless him and grant him peace, said to him: "O so-and-so, say: There is no god but Allah." He looked at his father, and his father remained silent. The Prophet, may Allah bless him and grant him peace, repeated it to him, and he looked at his father. His father said: "Obey Abu al-Qasim." The boy said: "I bear witness that there is no god but Allah, and that you are the Messenger of Allah." The Prophet, may Allah bless him and grant him peace, went out saying: "Praise be to Allah who saved him from the Fire through me."