Musnad Ahmad 865
It was narrated that ‘Ali (رضي الله عنه) said:
Abu Bakr (رضي الله عنه) used to recite in a low voice when he recited, and ‘Umar                            (رضي الله عنه) recited in a loud voice. When `Ammar (رضي الله عنه) recited, he would recite some from one soorah and some from another. That was mentioned to the Prophet (ﷺ) and he said to Abu Bakr (رضي الله عنه); `Why do you recite in a low voice?` He said: Because the One with Whom I am conversing can hear. He said to ʼUmar (رضي الله عنه): “why do you recite out loud?” He said: To scare the Shaitan and awaken those who are asleep. He said to ‘Ammar (رضي الله عنه): “Why do you recite some from one soorah and some from another?` He said: Do you hear me mixing with it something that is not part of it? He said: `No.` Then he said: `All of it is good.”
حَدَّثَنَا عَلِيُّ بْنُ بَحْرٍ، حَدَّثَنَا عِيسَى بْنُ يُونُسَ، حَدَّثَنَا زَكَرِيَّا، عَنْ أَبِي إِسْحَاقَ، عَنْ هَانِئِ بْنِ هَانِئٍ، عَنْ عَلِيٍّ، رَضِيَ اللَّهُ عَنْهُ قَالَ كَانَ أَبُو بَكْرٍ رَضِيَ اللَّهُ عَنْهُ يُخَافِتُ بِصَوْتِهِ إِذَا قَرَأَ وَكَانَ عُمَرُ رَضِيَ اللَّهُ عَنْهُ يَجْهَرُ بِقِرَاءَتِهِ وَكَانَ عَمَّارٌ رَضِيَ اللَّهُ عَنْهُ إِذَا قَرَأَ يَأْخُذُ مِنْ هَذِهِ السُّورَةِ وَهَذِهِ فَذُكِرَ ذَاكَ لِلنَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَقَالَ لِأَبِي بَكْرٍ رَضِيَ اللَّهُ عَنْهُ لِمَ تُخَافِتُ قَالَ إِنِّي لَأُسْمِعُ مَنْ أُنَاجِي وَقَالَ لِعُمَرَ رَضِيَ اللَّهُ عَنْهُ لِمَ تَجْهَرُ بِقِرَاءَتِكَ قَالَ أُفْزِعُ الشَّيْطَانَ وَأُوقِظُ الْوَسْنَانَ وَقَالَ لِعَمَّارٍ وَلِمَ تَأْخُذُ مِنْ هَذِهِ السُّورَةِ وَهَذِهِ قَالَ أَتَسْمَعُنِي أَخْلِطُ بِهِ مَا لَيْسَ مِنْهُ قَالَ لَا قَالَ فَكُلُّهُ طَيِّبٌ‏.‏