Telassar is mentioned twice in the Bible

Bible

The Bible refers to any one of the collections of the primary religious texts of Judaism and Christianity. There is no common version of the Bible, as the individual books , their contents and their order vary among denominations...

. First at 2nd Kings 19:12 (or according to the Greek Septuagent, 4th Kings 19:12), and secondly at Isaiah 37:12.

According to those two scriptures, Tel-assar was a place inhabited by “the people of Eden” and is mentioned along with Gozan

Gozan

Gozan may refer to:* The Ancient River Gozan, Amu Darya, The River Amu or Oxus, a river in North Afghanistan & Central Asia.* the Five Mountain System, a Japanese network of Zen temples...

 and Haran

Haran

Haran or Aran is a figure in Book of Genesis in the Hebrew Bible. Haran was born in Ur Kaśdim , the son of Terah and thus a descendant of Shem. Haran's brothers were Abram/Abraham and Nahor...

, which are in northern Mesopotamia

Mesopotamia

Mesopotamia is a toponym for the area of the Tigris–Euphrates river system, largely corresponding to modern-day Iraq, northeastern Syria, southeastern Turkey and southwestern Iran.Widely considered to be the cradle of civilization, Bronze Age Mesopotamia included Sumer and the...

, and Rezeph, the exact location of which is not known, several places having had this name. One such site, thought by some to have been part of an ancient district, is identified with modern Rusa’feh, located West of the Euphrates about 145 km (90 mi) South of modern Haran. It is thus in the vicinity of the suggested site of Gozan, with which Rezeph is mentioned. Sennacherib

Sennacherib

Sennacherib |Sîn]] has replaced brothers for me"; Aramaic: ) was the son of Sargon II, whom he succeeded on the throne of Assyria .-Rise to power:...

boasted, through his messengers, that the gods worshiped by the people of these places had been unable to deliver them from his forefathers.