Is it sufficient to say: "And I bear witness that Muhammad is the Messenger of Allah" instead of "His slave and His Messenger" in the Tashahhud?

The worshiper's saying in the Tashahhud, "And I bear witness that Muhammad is the Messenger of Allah," is sufficient and there is no harm in it, due to its establishment in some authentic forms of the Tashahhud. It has been reported from Ibn Abbas that the Messenger of Allah, peace and blessings be upon him, used to teach them the Tashahhud with this wording.