Musnad Ahmad 31:314

'Abd al-Rahman ibn Mahdi narrated to us, Isra'il narrated to us, from Abu Sinan, from Abu Salih al-Hanafi, from Abu Sa'id al-Khudri and Abu Hurayrah: That the Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Allah has chosen four phrases from speech: 'Subhan Allah' (Glory be to Allah), 'Al-hamdu lillah' (Praise be to Allah), 'La ilaha illa Allah' (There is no god but Allah), and 'Allahu Akbar' (Allah is the Greatest). Whoever says 'Subhan Allah', twenty good deeds are written for him, or twenty bad deeds are removed from him. Whoever says 'Allahu Akbar', it is the same as that. Whoever says 'La ilaha illa Allah', it is the same as that. And whoever says 'Al-hamdu lillahi Rabb al-'alamin' (Praise be to Allah, Lord of the worlds) from his own self, thirty good deeds are written for him, and thirty bad deeds are removed from him by it."