The noble wife of the Prophet Muhammad (peace be upon him), Sayyidah Hafsah (may Allah be pleased with her), narrates: I never saw the Prophet Muhammad (peace be upon him) performing voluntary prayers (nawafil) while sitting, until one year before his passing, I saw him performing voluntary prayers while sitting. He would recite the Surah slowly and with pauses, to the extent that it seemed even longer than the Surah itself.
Hadith Referenceصحیح ابن حبان / كتاب الصلاة / 2530
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - مضى (2499). تنبيه!! رقم (2499) = (2508) من «طبعة المؤسسة». - مدخل بيانات الشاملة -.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط مسلم.