Silsilat al-Ahadith al-Sahihah

Abu Bakr bin Abu Musa narrates from his father, who says: I came to the Prophet Muhammad (peace and blessings be upon him) with some members of my tribe. The Prophet (peace and blessings be upon him) said: "Rejoice and give glad tidings to those who come after you that whoever bears witness with a sincere heart that Allah alone is the true deity, he will enter Paradise." We left the Prophet (peace and blessings be upon him) to convey this glad tidings to the people, and we met Sayyiduna Umar bin Khattab (may Allah be pleased with him). (When he learned of the situation,) he sent us back to the Messenger of Allah (peace and blessings be upon him). The Messenger of Allah (peace and blessings be upon him) asked: "Who sent you back?" We said: Umar (may Allah be pleased with him) did. He asked: "Umar! Why did you send them back?" Sayyiduna Umar (may Allah be pleased with him) said: (If such glad tidings are given to the people,) they will rely on it (and abandon further deeds)." Upon hearing this, the Messenger of Allah (peace and blessings be upon him) remained silent.