´It was narrated hat Aishah said:` "The Messenger of Allah (ﷺ) used to pray standing and sitting. If he started to pray standing, he would bow standing and if he started to pray sitting, he would bow 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