Sahih al-Bukhari 4845

It is related that Ibn Abi Mulayka said, "The two good men were about to be destroyed: Abu Bakr and 'Umar. They raised their voices in the presence of the Prophet, may Allah bless him and grant him peace, when some riders from the Banu Tamim came to him. One of them suggested that he appoint al-Aqra' ibn Habis, the brother of the Banu Mujashi', and the other suggested someone else." (Nafi' said, "I do not remember his name.") He said, "Abu Bakr said to 'Umar, 'You just wanted to contradict me.' 'Umar said, "I did not want to contradict you," and they raised their voices over that. Allah then revealed, 'O you who believe! Do not raise your voices above the voice of the Prophet.' (49:1)" Ibn az-Zubayr said, "After that ayat 'Umar used to speak to the Messenger of Allah, may Allah bless him and grant him peace, in such a low voice so that he has to ask him to repeat it." Ibn az-Zubayr did not mention the same about his grandfather, i.e. Abu Bakr.