Sunan Abu Dawud
955
Sahih+3

‘A’ishah said:The Messenger of Allah (ﷺ) used to pray standing at night for a long time, and used to pray sitting at night for a long time. When he prayed standing, he bowed standing, and when he prayed sitting, he bowed sitting

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid