Majma al-Zawaid — Hadith 23

Ya'la bin Shaddad narrated: My father, Sayyiduna Shaddad (may Allah be pleased with him), narrated this hadith to me, while Sayyiduna Ubadah bin al-Samit (may Allah be pleased with him) was also present there and confirmed him (that is, my father, Sayyiduna Shaddad (may Allah be pleased with him)). My father said: We were with the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) asked: "Is there any stranger among you?" (The narrator said: By stranger) the Prophet (peace and blessings be upon him) meant the People of the Book. We said: "No, O Messenger of Allah!" The Prophet (peace and blessings be upon him) ordered that the door be closed and said: "Raise your hands and say La ilaha illallah (there is no god but Allah)!" We kept our hands raised for a while, then the Prophet (peace and blessings be upon him) lowered his blessed hand and said: "All praise belongs to Allah alone. O Allah, You have sent me with this word, commanded me with it and promised me Paradise for it, and You do not break the promise." Then he (peace and blessings be upon him) said: "Indeed, rejoice, for Allah Almighty has forgiven you."
Imam Ahmad, Imam al-Tabarani and Imam al-Bazzar recorded it, and its narrators have been declared trustworthy.