A master is bound to rehearse a lesson to his pupil four times.
Eiruvin, fol. 54, col. 2.
Alas for the power which prepares a grave for its possessor, for there is not a prophet who hath not in his lifetime witnessed the decadence of four kings; as it is said (Isa. i. 1), "The vision of Isaiah ... in the days of Uzziah, Jotham, Ahaz, and Hezekiah, kings of Judah" (see also Hosea i. 1).
P'sachim, fol. 87, col. 2.
Once Rav Pappa and Rav Hunnah partook together of a common meal, and as the latter ate only one morsel the former ate four. After this, when Rav Hunnah and Ravina ate together, the latter devoured eight portions to the other's one, upon which Rav Hunnah jocularly remarked, "A hundred (Rav) Pappas to one Ravina."
P'sachim, fol. 89, col. 2.
No food may be eaten on Passover-eve from the time of the offering of the evening sacrifice (in order, i.e. that abstinence may whet the appetite for the Matsoth). Even the poorest in Israel may not break his fast till the hour of reclining; nor is he to partake of less than four glasses of wine, even though he has been reduced so low as to subsist on the porridge doled out by public charity.
Ibid., fol. 99, col. 2.
There are four things the doing of which by man brings judgment upon his own head:—If he turn in between a wall and a date-palm; if he turn in between two date-palms; if he drink borrowed water; and if he step across spilt water, such even as his own wife may have thrown away. (All these doings, says Rashi, are bound to annoy the evil genii.)