Musnad Abu Ya'la al-Mawsili 152:279

Abu Khaythama narrated to us, al-Fadl ibn Dukayn narrated to us, Sayf ibn Abi Sulayman narrated to us, he said: I heard Mujahid say: Abu Ma'mar 'Abdullah ibn Sakhbara narrated to me, he said: I heard Ibn Mas'ud say: The Messenger of Allah (may Allah bless him and grant him peace) taught me the Tashahhud, [with] my palm between his palms, just as he would teach me a Surah from the Qur'an: "At-Tahiyyatu lillahi, was-salawatu, wat-tayyibatu. As-salamu 'alayka ayyuhan-Nabiyyu wa rahmatullahi wa barakatuhu. As-salamu 'alayna wa 'ala 'ibadillahis-salihin. Ash-hadu an la ilaha illallah, wa ash-hadu anna Muhammadan 'abduhu wa rasuluhu." And he was among us. Then, when he was taken [in death], we said: "As-salamu 'alan-Nabiyyi" (Peace be upon the Prophet), may Allah bless him and grant him peace.