Sayyiduna Abu Dharr (may Allah be pleased with him) narrates that I entered the mosque on Friday while the Prophet (peace and blessings of Allah be upon him) was delivering the sermon. So I sat near Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him), and the Prophet (peace and blessings of Allah be upon him) was reciting Surah Bara'ah (Tawbah). I asked Sayyiduna Ubayy (may Allah be pleased with him), "When was this Surah revealed?" He frowned at me and silenced me, and did not speak to me. After a while, I asked him again, so he sternly silenced me and did not speak to me. Then I remained silent for a little while, then I asked him again, so he frowned at me and silenced me and did not converse with me. Then, when the Prophet (peace and blessings of Allah be upon him) had finished the prayer, I asked Sayyiduna Ubayy (may Allah be pleased with him), "I asked you a question, but you frowned at me and silenced me and did not give me any answer." So Sayyiduna Ubayy (may Allah be pleased with him) said, "You have received no reward for your prayer except for your idle talk (sin)." Therefore, I went to the Prophet (peace and blessings of Allah be upon him) and submitted, "O Messenger of Allah, I was sitting beside Sayyiduna Ubayy (may Allah be pleased with him) while you were reciting Surah Bara'ah, so I asked him when this Surah was revealed, but he frowned at me and silenced me and did not give me any answer. Then he said, 'You have received no reward for your prayer except for this idle talk.'" So the Prophet (peace and blessings of Allah be upon him) said, "Ubayy has spoken the truth."