Musannaf Ibn Abi Shayba 21:298

Yahya ibn Abi Bukayr narrated to us, from Shu'bah, from al-Jurayri, from Abu 'Abd Allah al-Jasri, from 'Abd Allah ibn al-Samit, from Abu Dharr, who said: The Messenger of Allah (may Allah bless him and grant him peace) said to me: "Shall I not inform you of the most beloved speech to Allah?" I said: "O Messenger of Allah, inform me of the most beloved speech to Allah." He said: "Indeed, the most beloved speech to Allah is: *Subhan Allah wa bihamdihi* (Glory be to Allah and by His praise)."