It is narrated from Sayyidah Aishah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) would recite this supplication in his prostration: 'Subbuhun quddusun, rabbul-mala'ikati war-ruh' (Glorified and Most Holy is He, Lord of the angels and of the Spirit).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2683