Yahya related to me from Malik from Ibn Shihab from as-Sa'ib ibnYazid from al Muttalib ibn Abi Wadaa as-Sahmi that Hafsa, the wife ofthe Prophet, may Allah bless him and grant him peace, said, "I neversaw the Messenger of Allah, may Allah bless him and grant him peace,praying nawafil sitting, until a year before his death, when he beganto pray them sitting. He would recite the sura with a measuredslowness so that it would seem to be longer than other suras whichwere actually longer than it."
App reference: Book 8, Hadith 22
USC-MSA web (English) reference: Book 8, Hadith 22
Arabic reference: Book 8, Hadith 311