Midrash sur Rois 2 3:15

R. Juda the son of R. Samuel b. Shilath in the name of Rab said: "The sages wanted to suppress (declare uncanonical) the book of Ecclesiastes because its words are contradictory; but why did they not suppress it? Because it begins and ends with words concerning the Torah. It begins with the words concerning the Torah, for it is written (Ecc. 1, 3.) What profit hath a man of all his toil which he toileth under the sun? Whereupon the school of Janai said, for a thing which [was created] under the sun he hath no profit, but for a thing which is beyond the sun (before creation) he will have profit. It ends with words concerning the Torah, for it is written (Ib. 12, 13.) The end of the matter is, let us hear the whole; fear God and keep His commandments; for this is the whole (duty of) man. What is meant by, this is the whole man? R. Eliezer said: "It means the whole world was created for the sake of him (who fears God)." R. Abba b. Cahana said: "This [fear of God] is equal in importance to the whole world put together." Simon b. Azai and, according to others, Simon b. Zoma, said: "The whole world would not have been created if not for the purpose of providing him (who fears God) with company." And what are the words which contradict each other? It is written (Ecc. 7, 3.) Better is vexation than laughing; and again it is written (Ib. 2, 2.) Of laughter I said, it maketh one praiseworthy; and it is also written (Ib. 8, 15.) Therefore do I praise joy: and again (Ib. 2, 2.) And of joy what doth this do? There is no contradiction; Better is vexation than laughing, means that, the vexation which the Holy One, praised be He! causeth unto the righteous in this world is better than the smile which the Holy One, praised be He! causeth unto the wicked in this world; Of laughter I said, it maketh one praiseworthy, speaks of the smile with which the Holy One, praised be He! will gladden the righteous in the world to come. Therefore do I praise joyfulness, refers to a rejoicing which is caused by a meritorious deed; And of joy what doth this do? alludes to rejoicing which is not the cause of a meritorious deed. We infer from this that Shechinah rests not upon a mood of indolence, nor a mood of grief, nor a mood of laughter, nor a mood of levity, nor a mood of jesting, nor a mood of idle talk, but upon a mood of rejoicing caused by the performance of a meritorious deed; as it is said (II Kings 3, 15.) But now bring me a musician, etc, R. Juda said: "The same should be applied to the study of the Halacha (Laws)." Raba said: "The same is to be applied to a good dream." Is it so? [that Halacha should be preceded by a cheerful thing] . Behold, R. Gidel in the name of Rab said: "Any disciple who sits before his teacher without dropping bitterness from his lips [on account of respect] will be burnt, for it is said (Songs 5, 13.) His lips like lillies, dropping with fluid myrrh. Do not read Mor (fluid myrrh), but read it Mar (bitterness. Do not read Shoshanim (lilies) but read it Sheshonin (who study); [hence we see that a disciple must act with deep respect, and not in a frivolous mood]. This is not difficult to explain: the former refers to the teacher and the latter refers to the disciple; and if you wish you may say both refer to the teacher; and even then there is no contradiction; for the former refers to the time before beginning [the lecture] and the latter refers to the time after the lecture has begun. Just as Rabba did before he began [his lecture] before the Rabbis. He said something humorous which caused the Rabbis to be cheerful, and he then sat down with deep respect to expound the Halacha.

“Arise, cry out at night, at the beginning of the watches, pour out your heart like water before the face of the Lord. Lift up your hands to Him for the life of your infants, who are faint with hunger at the head of every street” (Lamentations 2:19).
“Arise, cry out at night, at the beginning of the watches.” Rabbi [Yehuda HaNasi] says: There are four watches during the night and four watches during the day. The ona is one twenty-fourth of the et,¹²³The text should read: The ona is one twenty-fourth of an hour (Etz Yosef). and the et is one twenty-fourth of the ona. The rega is one twenty-fourth of the et. How long is a rega? Rabbi Berekhya said in the name of Rabbi Ḥelbo: As long as it takes to say it. The Rabbis say: Like the blink of an eye. Shmuel said: One fifty-six thousand five hundred and forty-eighth of an hour; that is a rega. Rabbi Natan said: There are three watches during the night.
Rabbi Zerika and Rabbi Ami said in the name of Rabbi Shimon ben Lakish: One verse says: “At midnight I rise to give You thanks” (Psalms 119:62), and one verse says: “My eyes precede the night watches” (Psalms 119:148). How can these two verses be reconciled? Rabbi Ḥizkiya, and some say Rabbi Zerika and Rabbi Ami: One said the source according to Rabbi [Yehuda HaNasi] and one says the source according to Rabbi Natan. The one who says the source according to Rabbi [Yehuda HaNasi], it works out well.¹²⁴There are four watches during the night, two before midnight and two after midnight. Thus, if one rises at midnight, that is still before two of the nightly watches. These verses can thus be a source for the opinion of Rabbi Yehuda HaNasi that the night is divided into four watches. The one who says the source according to Rabbi Natan: “At the beginning of the middle watch” (Judges 7:19).¹²⁵If there is a middle watch, there must be an odd number of watches. This can serve as a source for the opinion of Rabbi Natan that the night is divided into three watches.
But Rabbi Natan, how does he interpret “at midnight”? Rather, at times “at midnight,” and at times: “My eyes precede the night watches.”¹²⁶The two verses do not both mean the same thing, as according to Rabbi Yehuda HaNasi. Rather, King David, the author of Psalms, is stating that at times he awoke at midnight, and at times even earlier, before two of the three nightly watches. What would [David] do? When David would conduct his meal alone, he would eat until nine hours of the day, sleep until the beginning of the middle watch, and arise and engage in Torah study. When David would eat a feast of kings, he would eat until the evening, sleep until midnight, and arise and engage in Torah study from midnight onward.
In any case, dawn would not arrive with David asleep. That is what David said: “Awaken, my soul, awaken, harp and lyre; I will wake the dawn” (Psalms 57:9). Let my honor awaken before the honor of my Creator; my honor is nothing before the honor of my Creator. “I will wake the dawn,” I wake the dawn, the dawn does not awaken me.
Rabbi Pinḥas said in the name of Rabbi Elazar bar Menaḥem: A lyre was placed under his head and he would rise and play it at night. Rabbi Levi said: A lyre was suspended over David’s bed. When midnight arrived, the north wind would come and the lyre would play on its own. That is what is written: “It was as the instrument played” (II Kings 3:15). It is not written here “It was as he played the instrument,” but rather: “It was as the instrument played,” the instrument played on its own. When David would hear its sound, he would arise and engage in Torah study. [People] would say: If David king of Israel is engaging in Torah study, all the more so for us. They immediately would begin engaging in Torah study.
How does Rabbi interpret the verse of Rabbi Natan? Rabbi Huna said: The end of the second and the beginning of the third, which constitutes the midpoint [metavḥot] of the night. Rabbi Mani said: Had it said “middle [tikhonot],”¹²⁷Had the verse used the plural term for “middle” that would allow for it to be interpreted in accordance with Rabbi Yehua HaNasi, who holds that the night is divided into four watches. that would be correct. But does it not say “middle [tikhona]”?¹²⁸This term is singular. The first is not counted, as until then, the time has not yet arrived.¹²⁹The concept of dividing the night into periods of time called watches parallels when an earthly king would have soldiers standing guard. The first quarter of the night is not yet the time for guards, because people are still awake.

Our Rabbis were taught that R. Eliezer says: "All the songs and praises which were uttered by David in tht Book of Psalms had reference to himself." But R. Joshua says: "David uttered them in reference to the community at large," while the sages maintain that there are some which he uttered in reference to himself and others which he uttered in reference to the community at large; viz., those which he uttered "in the singular number are in reference to himself and those which were uttered in the plural number were in reference to the commuity at large. The Psalms containing the term Nitzuach or Nigun were intended for the future world. The term Maskil means to indicate that it was said through a Methurgeman (interpreter). Unto David a song, signifies that the Shechina preceded the song and it caused him to sing. A song unto David, signifies that the song preceded the Shechina and caused it to rest upon David. This is to teach you that the Shechina does not rest on a person in a mood of idleness, nor in a mood of grief, nor in a mood of laughter, nor in a mood of levity, nor in a mood of jesting, nor in a mood of idle talk, but in a mood of rejoicing caused by performing a meritorious deed, as it is said (II Kings 3, 15) But now bring me a musician, and it came to pass, when the musician played, that the inspiration of the Lord came upon him, R. Juda, in the name of Rab, said: "The same should be applied to a good dream." Is it so? Has not R. Gidel said in the name of Rab: "Any student who sits before his teacher without dropping bitterness from his lips on account of respect will be burnt, for it is said (Songs 5, 13) His lips like lilies, dropping with fluid of myrrh. Do not read Shoshanim (lilies), but read it Sheshonim (who study); and do not read Mor Ober (with fluid myrrh), but Mar Ober (bitterness). [Hence we see that for Halacha a man must possess bitterness]. This is not difficult to understand. The former refers to the teacher and the latter refers to the scholar. And if you please, you may say both refer to the teacher, and still there is no difficulty in explaining it; the former applies to the time before the lecture begins, and the latter applies to the time when the lecture has already begun. Just as Rabba, before he started his lecture, would preface his remarks with something humorous, causing the scholars to feel good, and then proceed with sacredness in his course OL Halacha.