(9) And God said unto Moses: ‘Lo, I come to you in a thick cloud, that the people may hear when I speak with you, and may also believe in you for ever.’ And Moses told the words of the people to God. (10) And God said to Moses: ‘Go to the people, and sanctify them to-day and to-morrow, and let them wash their garments, (11) and be ready on the third day; for on the third day God will come down in the sight of all the people upon mount Sinai.

12th Century Spain 

Be Ready: Perhaps a person shouldn't sleep on them at night, because they will hear the voice of God in the morning, like the way of the Kohen Gadol on Yom Kippur.

6th Century Israel

... It is like a king, who said that he is coming on a particular day, and the people slept on the night before the king arrived.  He found them sleeping, and sounded trumpets to wake them up...  So too, the people of Israel slept all of the night before the giving of Torah ... because the sleep of the season is sweet, and the night is short.  Rav Yudan says, even a flea didn't bite them ... 

(1565) Tzfat, Israel

(1) The fiftieth day of the count of the Omer is the holiday of Shavuot. The order of prayer is like the holiday of Passover, rather we say "the Holiday of Shavuot, the time of the giving of our Torah". We say full Hallel. We take out two Torah scrolls and read in the first one five [sections] from "The third month" until the end of the order. The Maftir is read in the second scroll, "On the day of the first fruits". As Haftorah we read the chariot of Ezekiel, and end with the verse "and the wind took me up."

17th Century Poland

It is stated in the Zohar that on Shavuot the pious of former times would stay awake all night and engage in Torah study. The majority of Torah students (rov halomdim) have already adopted this practice. A reason for this which is based on the simple explanation, that the children of Israel slept all night [before the Torah was given] and the Holy One, Blessed be He needed to wake them [to receive the Torah.] as it says in the midrash. Consequently we are required to make amends (litaken) for this.

(3) Rabbi Shimon was sitting and studying the Torah on the night when the Bride, Malchut, unites with her husband, Zeir Anpin. And all the friends present in the bridal chamber on that night, the eve of the holiday of Shavuot, must stand together with the bridegroom under the Huppah, and be with him this whole night, and rejoice with him in the corrections of the Bride, i.e., study the Torah, then Prophets, then Holy Scriptures, and finally the wisdom, for these corrections are the Bride’s adornments. And the Bride receives corrections, adorns herself with them, and rejoices with them all of that night. And on the next day, on the holiday of Shavuot, she only comes to the Huppah together with them. And her friends, who studied the Torah all night long, are called the sons of the Huppah. And as she approaches the Huppah, the Creator asks about them, blesses and adorns them with the Bride’s adornments. Happy are those who merit this!

(4) This is why Rabbi Shimon and all of his friends stayed up that night, and each of them renewed the Torah again and again. Rabbi Shimon was joyous, and so were his friends. Rabbi Shimon said to them: “My sons, how blessed is your lot, for it is you who shall accompany the Bride tomorrow to the Huppah, for all those who correct Her and rejoice in Her this night shall have their names recorded in the Book of Remembrance. And the Creator shall bless them with seventy blessings and adornments of crowns of the Upper World.”

(5) Rabbi Shimon opened and said, (Ps. 19:2) “The Heavens declare the Creator’s greatness. I have already explained this, but when the bride awakens to enter the Huppah on the following day, with all the friends who rejoiced with her through that night, she rejoices with them, corrects herself and shines with her adornments.” And on the following day, a multitude of masses, hosts, and legions join her. And she, together with all these masses, hosts and legions, awaits all those who corrected her by studying the Torah on that night. This is so because Zeir Anpin unites with Malchut, and she sees her husband, and it is said: “The Heavens declare the Creator’s greatness.” “The Heavens” alludes to the Bridegroom (ZA), who enters the Huppah. “The Heavens declare,” i.e., shine, like the luminescence of a sapphire, upon the entire Malchut, from end to end.

(6) The Creator’s glory = EL – is the bride, Malchut, called EL, as it is written: (Ps. 7:12) “ EL rages each day.” She is called EL on all the days of the year. And now, on the holiday of Shavuot, when she already entered the Huppah, she is called GREATNESS and she is called EL, greatest of the great, luminescent out of the luminescent, dominion over dominions. The hour when the Heaven (ZA) enters the Huppah and shines upon Malchut, all of her friends, who corrected her by studying the Torah, are known by their names, as it is said: “The Heavens declare the work of His hands.” “The work of His hands” refers to the members of this covenant, called “the work of His hands.” As you say: “Confirm for us the work of our hands,” which is the mark of the covenant, imprinted on man’s body.

(7) Rabbi Hamnuna-Saba then said as follows: (Ecclesiastes 5:5) “Do not let your mouth cause your body to sin,” i.e., one must not allow his mouth to get close to evil and be the cause of sin for the sacred flesh, which bears the mark of the holy covenant with the Creator. If he does so, he shall be dragged to hell. And the ruler of hell, called Domeh, stands at the gates of hell with hundreds of thousands of angels, but he is forbidden to approach those who have kept the holy covenant in this world.

(8) When this happened to King David, fear enveloped him. Right then, Domeh ascended before the Creator, and said: “Master of the world,

(1) 'Master of the universe, in the Torah it says of "the man that commits adultery with another man's wife...the adulterer and the adulteress shall surely be put to death"' (Lev. 20:10). Furthermore, it is written, "Moreover, you shall not lie carnally with your neighbor's wife, to defile yourself with her" (Lev. 18:20). (So what is to become of) David, who has profaned his organ (of the holy covenant by committing a sexually immoral act)? The Holy One, blessed be He, said to him, "David is righteous! And the holy covenant remains intact, because it is known to Me that Bathsheba was assigned to him since the day the world was created.

(2) 2. (Domeh) then said: If this is known to you, it is not known to him. He (Hashem) said to him, 'Not only that, but all that happened was permitted and done lawfully. Because every man that went to war did not leave before he had given a bill of divorce to his wife!' He (Domeh) said to Him, If this is so, he should then have waited for three months, which he did not! Hashem replied: When is this applied? Only in cases where we suspect that she might be pregnant! And it is known to Me for certain that Uriah never touched her. Because My name is sealed in him as a witness. For it is written 'Uriah,' אוּרִיָּה. And it can also be written Uriahu (אוּרִיָּהוּ), 'to show that he is sealed by My Name that he never had intercourse with her.' Dumah said to Him, Master of the universe, this is exactly what I have said! If it is known to You that Uriah never slept with her, it is not known to him. Therefore, he should have waited for three months. And furthermore, if he knew that he had never slept with her, then why did he send Uriah home and command him to have intercourse with his wife? Since it is written: "Go down to your house and wash your feet" (II Samuel 11:8).

(3) 3. He said to Dumah, 'He certainly did not know. So he waited more than three months, as four months had passed.' Because we have learned that on the twenty-fifth day of Nissan, David sent an announcement (to go to war). And they were with Yoav on the seventh day of Sivan, as they went and destroyed the land of the children of Amon. There they remained during the months of Sivan, Tammuz, Av, and Elul. And on the twenty-fourth day of Elul the event with Batsheva occurred. Then on Yom Kipur (the Day of Atonement) the Holy One, blessed be He, forgave him for that sin. And there are those who claim that on the seventh day of Adar the announcement was sent, and all arms were gathered on the fifteenth day of Iyar. So what happened with Batsheva occurred on the fifteenth day of Elul. While on Yom Kipur, he received the message "Hashem also has put away your sin; you shall not die" (II Samuel 12:13). What is the meaning of "you shall not die?" It means that he shall not die at the hand of Dumah.

(4) 4. Dumah said, Master of the universe, I have one thing against him! He opened his mouth and said, "as Hashem lives, the man that has done this deserves to die" (Ibid. 5). So he has condemned himself to death, and therefore I have the power over him. He said to Dumah, You have no permission, because he has already confessed in front of Me saying, 'I have sinned against Hashem' even though he did not sin. Although his sin against Uriah was (by killing him), I have written his punishment and he has accepted it! Immediately Dumah returned to his place, disappointed. Concerning this David said, "Unless Hashem had been my help, my soul had almost dwelt in silence (Heb. דּוּמָה)" (Ps. 94:17). "Unless Hashem had been my help" that had He not become David's keeper and guarded him David's "soul had almost dwelt with Dumah." Why does he say "had almost?" Because only the smallest distance, as narrow as a thin thread separated him from the Other Side. So "almost dwelt with Dumah." Was just the distance of a thin thread away.

(5) 5. Therefore, every person should be careful not to say what King David said, because he will not be able to say to Dumah, "it was an error" (Eccl. 5:5), as it was with David. Because in David's case, the Holy One, blessed be He, defeated (Dumah) in the case. "Wherefore should Elohim be angry at your voice" (Ibid.) refers to the voice that said, "and destroy the work of your hands" (Ibid.). This is the sacred flesh, the holy covenant that he damaged, and because of which he is to be dragged down to Gehenom by the angel Dumah. And because of this, "the firmament proclaims His handiwork" (Ps. 19:2). These are the friends who have joined the Bride, (i.e. Malchut, by studying on Erev Shavuot), together with those who are the custodians of the sign of Her covenant. The firmament shows and registers each and every one of them. What is the firmament? It is where the sun, moon, stars and constellations are located, and it is the Book of Remembrance. It announces, registers, and inscribes them, so that they can be the residents of its own palace, and it can always fulfill their desires. "Day to day utters speech" (Ibid. 3) is an allusion to the sacred day that belongs to those supernal days of the King, that praise the friends. And they say to each other the same words that are written, "Day to day utters" that same "speech," thereby praising Him. The words "and night to night" refer to the levels that govern the night. They praise one another with the knowledge that each (receives) from its friends. And by this state of harmony and perfection, they become their friends and beloved ones.

(6) 6. "There is no speech nor language" (Ibid. 4). (This is) the speech and language that belong to worldly matters that are not heard before the Holy King, and that he is not interested in hearing them. But the words, "Their line is gone out through all the earth" (Ibid. 5),

(1) 1. that these words draw a line between the inhabitants of above and the inhabitants of below. From them, Firmaments are formed, and from them and from that praise, the earth is molded. And if you should say that these words wander around the world in one place, "and their words to the end of the world" (Ibid.). Because Firmaments are formed by them, who resides there? He repeated, "In them He set a tent for the sun" (Ibid.). That holy sun, (referring to Zeir Anpin), has made his habitation and above in them and crowned himself with them.