Al-Bazzar has recorded this from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him). Al-Aswad narrates: Sayyiduna Abdullah (may Allah be pleased with him) used to teach the words of the tashahhud during the prayer, and he would take care even over the alif and the waw.
In al-Tabarani's chain there is a narrator, Zuhayr bin Marwan al-Raqashi; I have not found anyone who mentions him. The narrators of al-Bazzar's chain are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2852