Musannaf Ibn Abi Shayba 21:749

Waki’ and Abu Dawud narrated to us, from Sufyan, from Salamah ibn Kuhayl, from Hilal, from Samurah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The best of speech is four: 'Subhan Allah' (Glory be to Allah), 'Al-hamdulillah' (Praise be to Allah), 'La ilaha illa Allah' (There is no god but Allah), and 'Allahu Akbar' (Allah is the Greatest). It does not matter with which of them you begin."