Musannaf Ibn Abi Shayba 21:139

Ghundar narrated to us, from Shu'bah, from Ziyad ibn Fayyad, who said: I heard Mus'ab ibn Sa'd, from Sa'd, that when he would perform the Tashahhud, he would say: "Glory be to Allah, filling the heavens and filling the earth and what is between them and what is beneath the soil." Shu'bah said: I do not know if "Allah is the Greatest" was before it, or "Praise be to Allah, a pure, blessed praise therein. There is no god but Allah alone, He has no partner. To Him belongs the dominion, and to Him belongs the praise, and He is capable of all things. O Allah, I ask You for all of the good." Then he would perform the Taslim.