"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).'"  

كَانَ رَسُولُ اللَّهِ ﷺ يَقُولُ فِي رُكُوعِهِ سُبُّوحٌ قُدُّوسٌ رَبُّ الْمَلاَئِكَةِ وَالرُّوحِ