Talmud zu Schemot 31:17

The Torah was given at Sinai through Moses' hands, as it says (Deuteronomy 5:19), "He wrote them on two stone tablets, and He gave them to me." And then later it says (Leviticus 26:46), "These are the decrees and the laws and the teachings that the Eternal gave, through Moses on Mount Sinai, between Him and the children of Israel." The Torah that the Holy Blessed One gave to Israel was given only through Moses, as it says (Exodus 31:17), "Between Me and the children of Israel"; Moses merited to be a messenger between the children of Israel and the Omnipresent God. Moses prepared the inaugural ram and the anointing oil, and anointed Aaron and his sons with it all seven days of inauguration, and from it, all the high priests and kings are anointed. And Elazar burned the [red] heifer as a sin offering, with which impurities would be purified for generations. Rabbi Eliezer said: Great is this ritual, for it is practiced throughout the generations, just as Aaron and his sons were sanctified with this anointing oil, as it says (Exodus 30:30), "Anoint Aaron and his sons, and sanctify them to serve as priests.”

‘For the Torah, [for the divine service],⁸¹M and H insert this phrase which is included in P.B. for the prophets and for this holy⁸²The ‘Sabbath’ or the name of the Festival is inserted here; and when a Festival coincides with the Sabbath both are mentioned. … which Thou, O Lord our God, hast given us for holiness and for rest, for honour and for glory. For all these things, O Lord our God, we thank Thee, and continually bless⁸³The P.B. version reads, ‘Thee, blessed be Thy name by the mouth of every living being continually and for ever’. Thy name, O God of our salvation. Blessed art Thou, O Lord, Who sanctifiest Israel and such and such a day.’⁸⁴For ‘such and such a day’ the name of the Festival is inserted.
An exception is made on the Sabbath when ‘Israel’ is not mentioned in the conclusion but only ‘Who sanctifiest the Sabbath’; because the Sabbath preceded Israel, as it is written, For in six days the Lord made heaven and earth, and on the seventh day He ceased from work and rested,⁸⁵Ex. 31, 17. and it is further said, See that the Lord hath given you the sabbath,⁸⁶ibid. XVI, 29. The Sabbath was instituted at the creation of the world, and the use of the definite article in the second quotation indicates that it was a well-known institution at the time. The Festivals, on the other hand, were ordained after the people of Israel came into existence. which implies that the Sabbath had already been in existence.

[What was the procedure in the case of] ma‘amadoth? As it was taught:¹⁸[Cf. Ta‘an. 27b (Sonc. ed., p. 145).] The men of the ma‘amadoth used to fast [as follows]: On every Monday for the sake of those who sail on the sea, as it is written, And God said: Let there be a firmament in the midst of the waters;¹⁹Gen. 1, 6. The mention of water is a call to prayer on behalf of those who sail over the sea. on Tuesdays for the sake of wayfarers, as it is written, And God said: Let the waters under the heaven be gathered together;²⁰ibid. 9, which is followed by And let the dry land appear. on Wednesdays for the sake of children that they should not be attacked by croup, as it is written, And God said: Let there be lights,²¹ibid. 14, children being to the home what the heavenly luminaries are to the world. the written form being defective;²²A waw is missing in the noun מארת (lights). on Thursdays they fasted for the sake of pregnant women and nursing mothers that they should not lose their children, as it is said, And God said: Let the waters swarm with swarms.²³ibid. 20, followed by living creatures (ibid.). On the Sabbath eve and at the conclusion of the Sabbath²⁴i.e. Sunday, as explicitly mentioned in Ta‘an. 26a (Sonc. ed., pp. 136f). they did not fast from respect for the Sabbath. Some declare²⁵As a reason why they did not fast on Sundays. that at the twilight of the Sabbath eve an additional soul is given to every Israelite, and after the Sabbath it is taken from him.²⁶The body is then weakened, and fasting is held to be too great a hardship. Another reason²⁷Why there was no fasting on Sunday. is that Christians²⁸So M and H. V has ‘worshippers of stars’, an alteration made because of the censor. should not say, ‘Because we rejoice on the Sunday they fast on it’. The Sages, however, said: In the period of the ma‘amadoth they were not concerned with the hatred of the Christians, but the reason is that it is written He ceased from work wayyinnafash,²⁹Ex. 31, 17, E.V., and rested. [which is homiletically interpreted] wai ‘al nefesh, ‘Woe for [the loss of the additional] soul’.