Ghudaif bin Harith reports: I asked Lady Aisha (may Allah be pleased with her): What do you say about the Prophet (peace be upon him)? Did he recite aloud or in a low voice while praying? Lady Aisha (may Allah be pleased with her) replied: Sometimes he would recite aloud and sometimes in a low voice. So I said: All praise is due to Allah, who has provided flexibility in this matter.
Hadith Referenceصحیح ابن حبان / كتاب الصلاة / 2582
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - انظر (2438). تنبيه!! رقم (2438) = (2447) من «طبعة المؤسسة». - مدخل بيانات الشاملة -.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح