ANSWER:

This is authentic as it was what Omer May Allah be pleased with him taught the people on the pulpit to say.

QUESTION: Is this form authentique for tashahud: At-taḥiyyātu lillāh, az-zakiyyātu lillāh, aṭ-ṭayyibātuṣ-ṣalawātu lillāh, as-salāmu ʿalayka ayyuhan-nabiyyu wa raḥmatullāhi wa barakātuh, as-salāmu ʿalaynā wa ʿalā ʿibādillāhiṣ-ṣāliḥīn, ash-hadu an lā ilāha illā Allāh, Wahdaho lā sharika lah wa ash-hadu anna Muḥammadan rasūlullāh.