Abu Hurairah reported,
When the verse was revealed, "Indeed, those who lower their voices in the presence of the Messenger of Allah" [Hujurat 49:3], Abu Bakr al-Siddiq said, "By the One who revealed the Book to you, Messenger of Allah, I will never speak to you except as one whispering a secret, until I meet Allah 
."
Azami 13340
Hasanعن أبي هريرة قال
لما نزلت: {إن الذين يغضون أصواتهم عند رسول الله} قال أبو بكر الصديق: والذي أنزل عليك الكتاب يا رسول الله لا أكلمك إلا كأخي السرار حتى ألقى الله عز وجل.
No references are available.
Hakim (2/461) and Bayhaqi in Shuab al-Iman (1431) both narrated it via Muhammad bin Amr bin Alqama, from Abu Salama bin Abdul-Rahman bin Awf, from Abu Hurairah, who said, and then he related it.Its chain is hasan because of Muhammad bin Amr bin Alqama, for he is hasan al-hadith.Hakim said, "This is a sahih hadith according to the criterion of Muslim."