It is narrated from Sayyiduna Abdur Rahman bin Abzi that once the Prophet (peace and blessings be upon him) was leading the Fajr prayer. During the recitation, one verse was omitted. After finishing the prayer, the Prophet (peace and blessings be upon him) asked, "Is Ubayy bin Ka'b among the worshippers?" Sayyiduna Ubayy bin Ka'b said, "O Messenger of Allah! Has such-and-such verse been abrogated or did you forget it?" The Prophet (peace and blessings be upon him) replied, "I forgot it."