Musannaf Ibn Abi Shayba 3:621

Abu Bakr narrated to us, he said: Hushaym ibn Bashir narrated to us, he said: Abd al-Rahman ibn Ishaq narrated to us, from Abu Burdah, from Abu Musa, who said: The Prophet (peace and blessings of Allah be upon him) said: "I have been given the beginnings of speech, its endings, and its comprehensive expressions." He said: We said, "Teach us from what Allah has taught you." He said: So he taught us the Tashahhud.