Venerable Bede in the year 731

Venerable Bede (672-735) wrote the Ecclesiastical History of the English People. He refers to the year 731 as the current year. "This is for the present the state of all Britain; about two hundred and eighty-live years after the coming of the English into Britain, and in the 731st year of our Lord".
http://www.ccel.org/ccel/bede/history.v.v.xxii.html. He refers to earlier historical years in his book, but this is almost certainly the earliest contemporaneous reference to dates in Anno Domini.