Musannaf Ibn Abi Shayba 21:314

Aswad ibn Amir narrated to us, Hammad ibn Salamah narrated to us, from Ali ibn Zayd, from Sa'id ibn al-Musayyib, who said: We were with Sa'd ibn Malik, and he remained silent for a moment. Then he said, "I have attained in this silence of mine the equivalent of what the Nile and the Euphrates have watered." We said, "And what have you attained?" He said, "Glory be to Allah (SubhanAllah), and praise be to Allah (Alhamdulillah), and there is no god but Allah (La ilaha illallah), and Allah is the Greatest (Allahu Akbar)."