Sunan an Nasai
1048
Sahih+2

It was narrated that Aishah said:"The Messenger of Allah (ﷺ) used to say when bowing: 'Subbuhun Quddusun Rabbul-mala'ikati war-ruh (Perfect, Most Holy, is the Lord of the angels and the spirit)

SahihAbu Ghuddah
SahihAl-Albani