صحیح بخاری · Hadith 4845

Narrated Ibn Abi Mulaika: The two righteous persons were about to be ruined. They were Abu Bakr and `Umar who raised their voices in the presence of the Prophet when a mission from Bani Tamim came to him. One of the two recommended Al-Aqra' bin Habeas, the brother of Bani Mujashi (to be their governor) while the other recommended somebody else. (Nafi`, the sub-narrator said, I do not remember his name). Abu Bakr said to `Umar, "You wanted nothing but to oppose me!" `Umar said, "I did not intend to oppose you." Their voices grew loud in that argument, so Allah revealed: 'O you who believe! Raise not your voices above the voice of the Prophet.' (49.2) Ibn Az-Zubair said, "Since the revelation of this Verse, `Umar used to speak in such a low tone that the Prophet had to ask him to repeat his statements." But Ibn Az-Zubair did not mention the same about his (maternal) grandfather (i.e. Abu Bakr).