When was the name אדני first used instead of the name יקוק?

Question

From this site we have a summary of the medrash:

As Yaakov nears his demise, the Torah tells us that he wanted to reveal to his children what was to transpire at the end of days. After Yaakov's plan is mentioned, the Torah continues to tell us that Yaakov called the brothers together to discuss their attributes and qualities. The Gemora tells us that suddenly his ability to prophesize left him, and he was unable to carry out his original plan. Startled by this sudden happening, Yaakov instantly attributed it to a flaw in his progeny, similar to that of Avrohom and Yitzchock, who each had a child who did not carry his legacy. The Shevatim, his children, immediately reacted by reciting the Shema and declaring their unanimous belief in the Oneness of HaShem.

I heard a Dvar Torah from the Brisker Rov which I did not totally understand. The point of it was that the brothers recited the Shema using the name אדני for the first name of Hashem and יקוק for the second like this

שמע ישראל אדני אלקנו יקוק אחד

This surprised me.

My main question is when was the name אדני first used instead of the name יקוק?

A secondary question is what was the full version of the Dvar Torah?

Please feel free to edit the question to make it clearer!

Answer 1

Wilhelm Bacher was an expert on this topic. In his magnificently researched article 'Shem Ha-Meforash' in Jewish Encyclopedia (online), he says,

The earliest instance of the dread of pronouncing the Tetragrammaton, and of the use of the paraphrasis "Adonai" instead, is found in the Septuagint rendering of Κύριος = "Lord."

As far as actual recorded legislation goes, he states,

The Mishnah (Soṭah vii. 6; Tamid vii. 2) says: "In the Sanctuary the name of God [in the three blessings, Num. vi. 24-26] is to be pronounced in the Priestly Benediction as it is written [יְהוָה]; but outside the Sanctuary it must be given the paraphrastic pronunciation [אֲדֹנָי].'. . .

The Mishnah (Berakot, end) mentions also an utterance of the Tetragrammaton outside the Sanctuary which was permitted and even commanded, saying that "it was ordained that the name of God should be used in the ordinary forms of greeting, which were the same as those exchanged between Boaz and the reapers [Ruth ii. 2], or the salutation of the angel to Gideon [Judges vi. 12]." According to Grätz ("Gesch." 2d ed., iv. 458), this injunction was given at the time of the Bar Kokba war, and the greeting, which contained the Tetragrammaton instead of the word "Adonai" (= "Lord"), was the shibboleth which distinguished the Jews from the Judæo-Christians, who regarded Jesus also as Lord. A haggadist of the third century, Abba bar Kahana, states (Midr. Teh. on Ps. xxxvi., end) that "two generations used the Shem ha-Meforash, the men of the Great Synagogue and those of the period of the 'shemad' [the Hadrianic persecution].

These details indicate that the long-sanctioned dread of uttering the Shem ha-Meforash was by no means without exceptions, and that the correct pronunciation was not unknown.

Answer 2

It appears that the name יקוק was never uttered other than Adnut, but in the Temple, as the Torah says:

1. "זֶה־שְּׁמִי לְעֹלָם וְזֶה זִכְרִי לְדֹר דֹּר׃" and Rashi explains - to "conceal" the "real" name.

2. "וְשַׁבְתֶּם אֵלַי וּשְׁמַרְתֶּם מִצְוֺתַי וַעֲשִׂיתֶם אֹתָם אִם־יִהְיֶה נִדַּחֲכֶם בִּקְצֵה הַשָּׁמַיִם מִשָּׁם אֲקַבְּצֵם וַהֲבִיאוֹתִים אֶל־הַמָּקוֹם אֲשֶׁר בָּחַרְתִּי לְשַׁכֵּן אֶת־שְׁמִי שָׁם׃"

In other words, all יקוק from Abraham to David were pronounced as אדני.

Answer 3

Shadal writes on Bereishit 2:4:

ולענין קריאת השם הזה אין ספק כי כל ימי בית ראשון וגם בתהילת בית שני היו קוראים אותו ככתבו, כי עינינו הרואות כמה שמות בני אדם מורכבים ממנו, יהונתן, יהוידע, יהושפט, יהורם, יהואחז, אחזיהו, חזקיהו, ישעיהו, ירמיהו, ועוד אם לא היו קוראים אותו למה יכתבוהו? ונראה כי בימי בית שני התקינו חכמים שלא לקרוא אותו ככתבו, ועשו זה אולי מפני שראו שהיו העם עוברים על לא תשא, שהיו מזכירים אותו לשוא, והתקינו שיהיו קוראים תחתיו שם אדנות

And as regards reading this name [יקוק], there is no doubt that during the entire first temple period, and also at the start of the second temple period they would read it as written. For our eyes see how many people's names were formed from it [e.g.] Yehonatan, Yehoyada, Yehoshaphat, Yehoram, Yehoachaz, Achazyahu, Chizkiyahu, Yeshayahu, Yirmiyahu. Furthermore, if it they would not read it, then why write it?

And it seems that during the second temple period the sages enacted not to read it as written. Perhaps they did this because they saw that people were viokating 'lo tisa' by taking G-d's Name in vain, and they therefore enacted to read instead of it the name אדנ-י.