One of the three phrases, along with Alhamdulillah and Allahu akbar, recited traditionally after prayers..
Origin
Mid 19th century; earliest use found in Edward Lane (1801–1876), orientalist. From Arabic subḥāna-llāh, lit. ‘the praise of God’ from subḥāna, probably the accusative of subḥān praise (only attested in this interjection) + allāh.