It is narrated from Sayyidah Aishah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) used to say in his bowing and prostration: 'Subbuhun quddusun rabbu al-mala'ikati wa al-ruh' (Most Glorious, Most Holy, Lord of the angels and of the Trustworthy Spirit).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2562