The God that Abraham worshiped is Jehovah, with his name in the Bible in the form of the Tetragrammaton, YHWH. The Tetragrammaton occurs 6,828 times in the Hebrew text printed in Biblia Hebraica and Biblia Hebraica Stuttgartensia. Abraham said to the King of Sodom: "I do lift up my hand in an oath to Jehovah (YHWH) the Most High God, Producer of heaven and earth, that, from a thread to a sandal lace, no, I shall take nothing from anything that is yours."(Gen 14:22, 23)
However, at some point a superstitious idea arose among the Jews that it was wrong even to pronounce the divine name (represented by the Tetragrammaton). Just what basis was originally assigned for discontinuing the use of the name is not definitely known. Some hold that the name was viewed as being too sacred for imperfect lips to speak. Yet the Hebrew Scriptures themselves give no evidence that any of Gods true servants ever felt any hesitancy about pronouncing his name. Non-Biblical Hebrew documents, such as the so-called Lachish Letters, show the name was used in regular correspondence in Palestine during the latter part of the seventh century B.C.E.
Many reference works have suggested that the name ceased to be used by about 300 B.C.E. Evidence for this date supposedly was found in the absence of the Tetragrammaton (or a transliteration of it) in the Greek Septuagint translation of the Hebrew Scriptures, commonly called the Old Testament, begun about 280 B.C.E. It is true that the most complete manuscript copies of the Septuagint now known do consistently follow the practice of substituting the Greek words Ky´ri·os (Lord) or The·os´ (God) for the Tetragrammaton. But these major manuscripts date back only as far as the fourth and fifth centuries C.E.
More ancient copies, though in fragmentary form, have been discovered that prove that the earliest copies of the Septuagint did contain the divine name, such as the fragmentary remains of a papyrus roll of a portion of Deuteronomy, listed as P. Fouad Inventory No. 266. It regularly presents the Tetragrammaton, written in square Hebrew characters, in each case of its appearance in the Hebrew text being translated. This papyrus is dated by scholars as being from the first century B.C.E., and thus it was written four or five centuries earlier than the manuscripts mentioned previously.
The Jewish Mishnah, a collection of rabbinic teachings and traditions, is somewhat more explicit. Some of the Mishnaic traditions concerning the pronouncing of the divine name are as follows:
In connection with the annual Day of Atonement, Danbys translation of the Mishnah states: And when the priests and the people which stood in the Temple Court heard the Expressed Name come forth from the mouth of the High Priest, they used to kneel and bow themselves and fall down on their faces and say, Blessed be the name of the glory of his kingdom for ever and ever! (Yoma 6:2) Of the daily priestly blessings, Sotah 7:6 says: In the Temple they pronounced the Name as it was written, but in the provinces by a substituted word.
Sanhedrin 7:5 states that a blasphemer was not guilty unless he pronounced the Name, and that in a trial involving a charge of blasphemy a substitute name was used until all the evidence had been heard; then the chief witness was asked privately to say expressly what he had heard, presumably employing the divine name. Sanhedrin 10:1, in listing those that have no share in the world to come, states: Abba Saul says: Also he that pronounces the Name with its proper letters. Yet, despite these negative views, one also finds in the first section of the Mishnah the positive injunction that a man should salute his fellow with [the use of] the Name [of God], the example of Boaz (Ruth 2:4) then being cited.Berakhot 9:5.
Taken for what they are worth, these traditional views may reveal a superstitious tendency to avoid using the divine name sometime before Jerusalems temple was destroyed in 70 C.E. Even then, it is primarily the priests who are explicitly said to have used a substitute name in place of the divine name, and that only in the provinces.
(source of information - Insight on the Scriptures, vol. 2)