Shabbath, fol. 152, col. 2.
The Rabbis have taught that a man should not drink water on Wednesdays and Saturdays after night-fall, for if he does, his blood, because of risk, will be upon his own head. What risk? That from an evil spirit who on these evenings prowls abroad. But if the man be thirsty, what is he to do? Let him repeat over the water the seven voices ascribed to the Lord by David in Psalm xxix. 3-9, "The voice of the Lord is upon the waters," etc.
P'sachim, fol. 112, col. 1.
Seven precepts did Rabbi Akiva give to his son Rabbi Yehoshua:—(1.) My son, teach not in the highest place of the city; (2.) Dwell not in a city where the leading men are disciples of the wise; (3.) Enter not suddenly into thine own house, and of course not into thy neighbor's; (4.) Do not go about without shoes; (5.) Rise early and eat in summer time because of the heat, and in winter time because of the cold; (6.) Make thy Sabbath as a week-day rather than depend for support on other people; (7.) Strive to keep on close friendly terms with the man whom fortune favors (lit. on whom the present hour smiles). Rav Pappa adds, "This does not refer to buying or selling, but to partnership."
Ibid.
How is it proved that mourning should be kept up for seven days? It is written (Amos viii. 10), "I will turn your feasts into mourning," and these in many cases lasted seven days.
Moed Katon, fol 20, col. 1.
Rav Chisda said there are seven kinds of gold:—Gold, good gold, the gold of Ophir, purified gold, beaten gold, shut-up gold, and gold of Parvain.
Yoma fol. 44, col. 2.