Aishah 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.
Related hadith on this topic
Explanation & Benefits
Shaykh Umar Farooq Saeedi
955. Commentary:
The best practice is that when the recitation (qira’ah) is performed standing, then the bowing (ruku‘) should also be performed standing; and if the recitation is performed sitting, then the bowing should also be performed sitting... This, and the aforementioned scenario—i.e., if a portion of the rak‘ah is performed standing and a portion sitting—is also permissible.
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 955