﴿ إِنَّ ٱلَّذِينَ يَغُضُّونَ أَصْوَٰتَهُمْ عِندَ رَسُولِ ٱللَّهِ أُو۟لَٰٓئِكَ ٱلَّذِينَ ٱمْتَحَنَ ٱللَّهُ قُلُوبَهُمْ لِلتَّقْوَىٰ ۚ لَهُم مَّغْفِرَةٌۭ وَأَجْرٌ عَظِيمٌ ﴾

“Behold, they who lower their voices in the presence of God’s Apostle - it is they whose hearts God has tested [and opened] to consciousness of Himself; [and] theirs shall be forgiveness and a reward supreme.”

(Lo! they who subdue their voices) this also was revealed about Thabit Ibn Qays Ibn Shammas after he was prohibited from raising his voice (in the presence of the Messenger of Allah) Allah bless him and give him peace, praising him for lowering his voice in the presence of the Prophet (pbuh) saying: they who subdue their voice in the presence of the Messenger of Allah (those are they whose hearts Allah hath proven) those are they whose hearts Allah has cleansed and purified (unto righteousness) from sin; it is also said that this means: those are they whose hearts Allah has made sincere to the profession of Allah's divine Oneness. (Theirs will be forgiveness) of their sins in the life of the world (and immense reward) and abundant reward in the Garden.