Muwatta Malik Book 8, Hadith 19
Yahya related to me from Malik from Hisham ibn Urwa from his
father that the Messenger of Allah, may Allah bless him and grant him
peace, came out during his illness, and approached and found Abu Bakr
standing, leading the people in prayer. Abu Bakr began to go back, but
the Messenger of Allah, may Allah bless him and grant him peace,
indicated to him to stay where he was. The Messenger of Allah, may
Allah bless him and grant him peace, sat by the side of Abu Bakr, and
Abu Bakr prayed following the prayer of the Messenger of Allah, may
Allah bless him and grant him peace, who was sitting, and the people
prayed following the prayer of Abu Bakr.
Yahya related to me from Malik from Hisham ibn Urwa from his father that A'isha, the wife of the Prophet, may Allah bless him and grant him peace, said, "The Messenger of Allah, may Allah bless him and grant him peace, prayed while he was ill. He prayed sitting, and some people prayed behind him standing, and he indicated to them to sit down. When he left, he said, 'The imam is only appointed to be followed. When he goes into ruku, go into ruku and when he rises, rise and if he prays sitting, pray sitting .' "
Yahya related to me from Malik from Ismail ibn Muhammad ibn Said ibn Abi Waqqas from a mawla of Amr ibn al-As or of Abdullah ibn Amr ibn al-As that the Messenger of Allah, may Allah bless him and grant him peace, said, "The prayer of one of you sitting down is only equal to half the prayer of one of you when he is standing."