Musnad Ahmad 1155:21

Muhammad ibn Bakr narrated to us, he said: Ibn Jurayj informed us, he said: Ibn Shihab said, and 'Ata' ibn Yazid informed me that al-Muttalib ibn Abi Wada'ah informed him that Hafsa, the wife of the Prophet, may God bless him and grant him peace, informed him, she said: "I did not see the Messenger of God, may God bless him and grant him peace, praying while sitting until it was a year or two before his death."