Sayyiduna Ammar bin Yasir (may Allah be pleased with him) narrates: Sayyiduna Abu Bakr (may Allah be pleased with him) was asked: "Why do you recite in a low voice?" He replied: "I make the One with whom I am conversing hear me." Sayyiduna Umar (may Allah be pleased with him) was asked: "Why do you recite aloud?" He said: "I wake up the sleeper." Another man was asked: "Why do you mix (different surahs) in your recitation?" He said: "Have you heard me add anything to it that is not part of it?" He replied: "No." He said: "These are pure and good things, which I mix with one another."
Al-Tabarani recorded it in al-Mu'jam al-Kabir; its chain contains Ayyub bin Jabir, whom Ahmad and Amr bin Ali declared thiqah (trustworthy), while Ibn al-Madini and Ibn Ma'in declared him da'if (weak).